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Archive for the ‘Meteorology’ Category

Thunderstorms, Tornadoes, Ice Storms, Avalanches

HAMweather Advisory Center

HAMweather Advisory Center

HAMweather Radar Center Southeastern U.S.

HAMweather Radar Center Southeastern U.S.

HAMweather Advisory Center

HAMweather Advisory Center

HAMweather Advisory Center

HAMweather Advisory Center

Snow in Chehalis, WA credit: Jude3 - komonews.com

Snow in Chehalis, WA credit: Jude3 - komonews.com


The thunderstorm threat we discussed yesterday has evolved in the deep south, with a tornado watch that extends from southeastern Mississippi through the midlands of Alabama to the northeastern extent of the state. Shear exhibits the same trends as discussed, where vertical profiles favor linear formations with embedded supercells and the possibility of tornadoes due to low level shear even with the marginal thermodynamics. The threat will continue through the evening as the line continues to move east, with the additional threat of flash flooding.

At the time of this writing, our Advisory Center (note top left) shows flash flood warnings, areal flood warnings, and flash flood watches for most of Mississippi and Alabama where rainfall totals have averaged between 2-4″ with locally higher amounts. Reports of roadways becoming impassable have already surfaced, please do not try to drive through them if you are in the area.

The mixed precipitation of freezing rain / sleet we discussed yesterday is continuing on its forecast trek through the northeast. Freezing rain advisories and ice storm warnings have popped up in the forecast zones. A sample ice storm warning appears as follows:

–[snip]–
AN ICE STORM WARNING REMAINS IN EFFECT UNTIL 1 PM EST WEDNESDAY….

WINTRY PRECIPITATION WILL CONTINUE ACROSS THE REGION THROUGH THE AFTERNOON HOURS. FOLLOWING A BRIEF PERIOD OF SNOW AND SLEET. A PROLONGED PERIOD OF SLEET WILL OCCUR DURING THE VERY LATE AFTERNOON AND EVENING HOURS BEFORE GRADUALLY MIXING WITH AND CHANGING TO FREEZING RAIN LATER TONIGHT. A SIGNIFICANT
ACCUMULATION OF ICE BETWEEN ONE QUARTER AND ONE HALF OF AN INCH IS LIKELY OVERNIGHT…
–[snip]–

Heavy snows will continue for the northern Rockies over the next few days as Pacific moisture continues to funnel into the region. As mentioned yesterday snow levels are at higher levels (6k or so), however it is very likely that accumulations will surge past the foot mark, approaching two feet. Previous accumulations and high freezing levels have cause avalanche warnings to be issued for much of the pacific northwest, with the unusual use of the word “many” in the warning below:


–[snip]–
…AVALANCHE WARNING FOR EXTREME AVALANCHE DANGER TUESDAY AFTERNOON THROUGH WEDNESDAY AFTERNOON…

INCREASINGLY HEAVY SNOW OR RAIN RISING FREEZING LEVELS AND
INCREASING WINDS SHOULD SPREAD TO MOST AREAS LATER TUESDAY MORNING AND AFTERNOON. THIS SHOULD BE FOLLOWED BY HEAVY TO VERY HEAVY RAIN OR SNOW RELATIVELY HIGH FREEZING LEVELS AND STRONG WINDS TUESDAY NIGHT AND WEDNESDAY. SUCH WEATHER SHOULD SEVERELY STRESS THE 20 TO OVER 50 INCHES OF RECENT LOWER DENSITY AND GENERALLY WEAKER SNOW RECEIVED SINCE THE LAST MAJOR WARMUP ON DEC 31ST. CURRENTLY UNSTABLE SNOWPACK CONDITIONS SHOULD WORSEN CONSIDERABLY OVER THE NEXT 36
HOURS WITH EXTREME AVALANCHE DANGER DEVELOPING ABOVE ABOUT 4 TO 5000 FEET AND GENERALLY HIGH DANGER CONTINUING OR INCREASING AT LOWER ELEVATIONS.

MANY NATURAL OR HUMAN TRIGGERED SLIDES SHOULD BECOME CERTAIN TUESDAY AFTERNOON THROUGH WEDNESDAY ALONG WITH AN INCREASING POTENTIAL FOR SOME LARGE DESTRUCTIVE AVALANCHES. SUCH AVALANCHES MAY INVOLVE MOST OF THIS SEASONS SNOWPACK AND RANGE UP TO 6 TO 10 FEET OR MORE. ALTHOUGH THE GREATEST LIKELIHOOD OF CLIMAX AVALANCHES RELEASING TO THE GROUND IS EXPECTED ALONG THE CASCADE EAST SLOPES AND THE NORTHEAST WASHINGTON CASCADES THE OVERWHELMING AMOUNT OF STRESS ON
BUREID WEAK LAYERS SHOULD PRODUCE VERY DANGEROUS CONDITIONS AND RELATIVELY LARGE AVALANCHES IN A VARIETY OF LOCATIONS.

AS A RESULT BACK COUNTRY TRAVEL IN AVALANCHE TERRAIN SHOULD BE AVOIDED TUESDAY AFTERNON THROUGH WEDNESDAY EVENING AND TRAVELERS SHOULD CONFINE TRAVEL TO RELATIVELY FLAT TERRAIN WELL AWAY FROM AVALANCHE PATH RUNOUTS.

NOTE THAT NO CONTROL WORK IS PERFORMED OUTSIDE OF HIGHWAY CORRIDORS AND SKI AREA BOUNDARIES SO EXPECT BACK COUNTRY CONDITIONS WHEN LEAVING SUCH AREAS. THIS STATEMENT WILL BE UPDATED AS CONDITIONS WARRANT. PLEASE VISIT WWW.NWAC.US FOR DETAILS.

–[snip]–


Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

Snow, Rain, Freezing Rain, Tornadoes?

Forecast Temperatures Animation

Forecast Temperatures Animation

Forecast Precipitation Type Animation

Forecast Precipitation Type Animation

Deep bitter arctic cold opens the first work week of the new year for the Northern Great Plains and higher elevations of the Rockies (temperature animation). Fortunately those temperatures will move out fairly quickly, affording locations such as Rapid City, South Dakota (forecast) to see temperatures above freezing for the balance of the week! On the other side of the temperature spectrum Miami, Florida will continue to bask in the warm glow of tropical temperatures with highs in the 80s through Wednesday, then cooling a bit with highs only in the mid 70s Thursday and Friday (forecast).

Another opportunity for freezing rain and sleet also opens the first week of the new year, with the mixed precipitation beginning in central Texas today, and moving northeast in the direction of the Nation’s Capital by Wednesday Morning. While accumulations are expected in Texas and Arkansas, the heaviest totals with this system will be in Northern Virginia, West Virginia, and southern Pennsylvania. This morning’s precipitation type forecast product will give you an idea of the progression of the system.

The Pacific Northwest will continue to be pummeled with snow as a strong jet funnels in copious amounts of moisture, while eastward facing slopes will experience additional enhancement with a 45 knot low level jet, increasing upslope snows. Temperatures are such that most snowfall will be above the 3000 foot range initially, but warmer temperatures will accompany the westerly winds allowing the threshold to climb to around 6000 feet or so later today. You may view our precipitation type animation to gain a better feel.

The south will be facing rains today and tomorrow, with the potential for thunderstorms tomorrow as well. At the moment, instability appears to be marginal, but shear is reasonably impressive at least in the vertical. This translates to the likelihood of linear bowing structures with embedded supercells, with accompanying wind threat and perhaps tornadoes since low level shear is present at the forecast level.

Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

PNW In For a Blow, Another Ice Storm On the Way?

HAMweather Advisory Center

HAMweather Advisory Center

The Ice Man Cometh?

The Ice Man Cometh?


Over the next few days the Pacific Northwest will be pounded yet again with heavy snow and rain as a strong pacific jet funnels moisture into the region. Heaviest snows will of course be in the mountainous regions of Washington, Northern Idaho, and Northwest Wyoming, with new accumulations reaching well above the two foot mark, and likely reaching more than three.

Also a concern with this system is flooding in the lower elevations and coastal regions of the PNW, as our Advisory Center shows, flood watches have already been posted calling for rainfall totals up to 3″ in the valleys, and up to 7″ along the coastal range.

Significant snows will not occur over the next few days for the rest of the country, however a dusting along the northern tier will occur as a weak low ambles through. The interesting story is over the weekend however.

In running our HAMweather Precipitation Type forecast product this afternoon, a possibility for another ice storm seems to be in the future. I have created a loop of the product here for you to view, that allows you control of the animation with such parameters as speed, single frame advancement, and so forth.

When viewing the product note the timestamp on the bottom of “Valid Time,” and the red swath that appears in the middle of the country late Saturday evening into Sunday morning where the animation ends. It seems the models have an idea the possibility of freezing rain / sleet / mixed precipitation is in store for the region before the weekend is out, so if you have travel plans, please stay abreast of weather conditions because if she does come together it could be an ugly situation =)

New Years Eve Midnight Forecasts for Select Cities:

  • London, England: Clear Skies, -2ºC, NE winds ~ 10kts - Full Forecast
  • New York, NY: Cloudy Skies, 29°F, Light SE Winds - Full Forecast
  • Chicago, IL: Cloudy Skies, 36°F, S Winds ~ 9mph - Full Forecast
  • Phoenix, AZ: Partly Cloudy, 55°F, Light NW Winds ~ 5mph - Full Forecast
  • Los Angeles, CA: Clear Skies, 55°F, Calm Winds - Full Forecast
  • Honolulu, HI: Partly Cloudy, 72°F, light NE winds - Full Forecast

Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

Where is This Slop Going? Will it Snow Christmas Day?

Precipitation Type Animation - Click for Full Size

Precipitation Type Animation - Click for Full Size

Precipitation Type Forecast Christmas Morning - Click for Full Size

Precipitation Type Forecast Christmas Morning - Click for Full Size


Quick update on the transition of the precipitation pattern over America’s Heartland. For the last few days we have discussed the mix of snow, freezing rain, and liquid precipitation that will truck along the central United States to exit the country through the eastern Great Lakes and New England.

The question is, where will it snow, where will their be a mix of slop, and where will it rain?

In the early morning post we showed you a quick glance of forecast snowdepth, so for this late morning post I thought you might enjoy a look at forecast precipitation type based upon the 12z model run. There are four fields in this product, where precipitation type is defined as either liquid precipitation, snow, freezing rain, or sleet.

To view the animation select the image above left, or click here. Notice the swath of greens, reds, purples, and whites that flow in a general northeastern direction beginning in the southcentral United States (note legend on the graphic where green is rain, white snow etc). This is the progression of the surface low we have been discussing. On this morning’s 12z run, notice that the transition of liquid precipitation and snow is further north than it was, even from the 06z run. This is not an uncommon occurrence as models try to balance out the dynamics of a system, small transitory shifts with forecasts of conditions at the surface nearly always occur.

Also notice that as the first batch of weather moves through, another is forecast for the northern great plains beginning late Thursday evening to Friday morning, where a range from the upper great plains to the midwest will experience another glorious mix of winter muck =)

Of course the Pacific Northwest can’t be left out of the mix, as Christmas Eve ushers in another influx of snow that will transition through the Rockies, with rain falling from the central California Valley all along the southern coast.

Just for grins and giggle I also posted a forecast precipitation type graphic for Christmas Morning. Select the graphic at top right, or click here to see if the early morning conditions are what you want, or turn out as they were forecast! Of course if you want to see precipitation types throughout Christmas day, refer to the animation and note the valid time stamp at the bottom of the graphic.

Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

Snow, Bitter Cold, With More to Come!

WRF/NAM 2 Meter Temperature Animation

WRF/NAM 2 Meter Temperature Animation

Today's Outlook

Today's Outlook

Christmas Eve Mess

Christmas Eve Mess

Denise LaPorte's Dog Riley Gives His Thoughts on Winter

Denise LaPorte's Dog Riley Gives His Thoughts on Winter - Chicago Tribune

Christmas Lights Under The Snow Credit: Digmunster - KOMONEWS

Christmas Lights Under The Snow Credit: Digmunster - KOMONEWS

Travel was interrupted throughout many regions of the nation over the weekend from the Pacific Northwest to America’s Heartland as planes, trains, and automobiles were dealt heavy blows of snow and bitter cold, that will unfortunately continue for a bit longer.

To give an overview of temperatures through the first part of Christmas morning, we have our WRF/NAM 2 Meter Surface Temperature Animation that can be viewed full size by either clicking here, or the graphic at top left (feel free to link to, or use the image on your site as long as it remains unaltered).

The animation represents this morning’s 06z run, and at initialization clearly depicts the massive jolt of arctic air trapped in the nation’s midsection this morning. I can attest to this fact, as this morning as I went out for my morning latte and bagel, the outdoor temperature sensor on my Lincoln said “2°F,” and it definitely did not want to start. It was the scenario where the car barely turns over once, and you ask yourself: “Is a latte really worth this?” Then of course, you keep the key turned and eventually the car turns over if you’re lucky. Fortunately for me it did, and after my latte my typing speed has increased by about 40wpm =)

Watch the animation closely as the 0°F temperatures and below (purple colors) slowly stream out of the Midwest to be replaced by above freezing (note the small red TOI {temperature of interest} line that indicates the freezing mark 32°F) temperatures. Fortunately the subzero temperatures will mostly exit the country to be replaced by something a little more bearable, other than the highest elevations of the Rockies and the extreme northern Tier.

The reason warmer air will advect into the midwest is a surface low that will slowly build and move in the general direction of the Great Lakes. As usual the exact path is somewhat difficult to discern, but at this point models tend to agree that the center of the low will pass close to Chicago Proper.

When this type of setup occurs at this time of year, it brings a mixture of precipitation types, with snow on the northern edge, mixed freezing rain / sleet in the middle of a dividing line with liquid precipitation on the southern edge. In the graphic at left I have generalized the areas of projected precipitation associated with the surface low as a strong influx of gulf moisture will stream into the midwest. One key with this setup will be the marriage of surface temperatures with those aloft, as it is likely that a wide area of freezing rain and sleet will occur, however if temperatures should continue to rise as the low pushes further north, freezing rain and sleet should migrate over to all liquid precipitation.

The Pacific Northwest will continue to be bombarded through Wednesday as a nice split flow setup invades the region. Today areas all across the Rockies an upper trough will continue to lower heights as moisture rides the Pacific Train into the region spurring very heavy orographic snow along all of the mountainous terrain from the central Rockies through the Pacific Northwest, where as usual the Cascades will receive at least a foot of snow, along with the Sierras and San Juan Mountains and Colorado Rockies.

The Key for the Pacific Northwest is what is to come… again =) Most of tomorrow will be fairly quiet, however a nice split flow regime will invade on Tuesday evening through Wednesday, where snows will begin across northern California and into the Sierras, but by Wednesday the split flow will give way to an intensified trough allowing for an absurd amount of Pacific moisture to invade the region with once again well over a foot of snow for the Cascades, and a chance of snow for Seattle.

Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick