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Jan 17-19 Mid-Atlantic obs/disco


Ian

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Although talk about hedging their bets. According to my LWX forecast, we could have all ice or rain till noon, or a combination of both, or nothing, or snow, or drizzle...I'm dizzy from just reading that.

Tonight: Freezing rain and sleet before midnight, then freezing rain between midnight and 3am, then rain or freezing rain after 3am. Low around 30. East wind around 9 mph. Chance of precipitation is 100%. Total nighttime ice accumulation of less than a 0.1 of an inch possible. Total nighttime sleet accumulation of less than a half inch possible.

Tuesday: Rain or freezing rain before noon, then a chance of rain between noon and 3pm. High near 39. North wind between 8 and 10 mph. Chance of precipitation is 100%. Little or no ice accumulation expected

Point and click forecasts are largely automated.. stop with the over-analyzation

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I don't see anything that supports areas NW of 95 turning to rain. This could be a pretty major ice storm for the area.

http://snowball.millersville.edu/~cws/SpecialWeatherDiscussion.html

Someone else agrees with you too.

7:00pm Monday update:

I really think some forecasters are underplaying this event. It's really a classic set up for an icy mess. Temperatures didn't hardly rise today...a sign of the strong cold air damming in place across the region. Also, dew points remain in the singles and teens early this evening, so the air will cool a bit more when precipitation arrives. Still looks like light snow will develop by mid-evening, and become steady before midnight. An inch or two of snow is possible, but the bigger concern is ice build-up on trees, powerlines, and untreated roads...later tonight into midday Tuesday. A 1/4" of ice (perhaps more in spots) is possible by mid-morning Tuesday, as temps only slowly rise towards 32 degrees. The steady precip will likely end around Noon, and so mos--or all--of the event will occur with below freezing temps. Thus, my concern for a pretty significant event the next 18 hours...one that I think deserves a Winter Storm Warning from the NWS (we are only in a lesser "Advisory", though).

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MESOSCALE DISCUSSION 0028

NWS STORM PREDICTION CENTER NORMAN OK

0644 PM CST MON JAN 17 2011

AREAS AFFECTED...NRN VA...CNTRL MD...WASHINGTON D.C.

CONCERNING...WINTER MIXED PRECIPITATION

VALID 180044Z - 180645Z

A SWATH OF PRECIPITATION WILL EXPAND NWD INTO NRN VA/MD AND THE

WASHINGTON D.C. METRO AREA THIS EVENING...WITH INITIAL P-TYPES OF

SNOW/SLEET EXPECTED TO TRANSITION TO FREEZING RAIN. LIQUID

PRECIPITATION RATES OF 0.05-0.10 IN/HR WITH LOCALLY HIGHER AMOUNTS

SHOULD PERSIST INTO THE EARLY MORNING.

WEAK ASCENT OCCURRING WITHIN A LOW-LEVEL WARM ADVECTION REGIME

/PRIMARILY CONFINED TO THE 900-800 MB LAYER/ WILL RESULT IN AN

EXPANSION OF A LARGE SWATH OF PRECIPITATION CURRENTLY OBSERVED OVER

SERN VA. SFC OBSERVATIONS INDICATE LARGE T-TD SPREADS VARYING

BETWEEN 10-20 DEG F ACROSS MUCH OF NRN VA AND CNTRL MD...WITH

TEMPERATURES GENERALLY IN THE LOWER-MID 30S. 00Z IAD RAOB INDICATES

THE THERMODYNAMIC PROFILE IS ENTIRELY BELOW FREEZING /SUPPORTIVE OF

SNOW/...AND IS SLIGHTLY COLDER IN THE 900-850 MB LAYER THAN NEARLY

ALL MODEL POINT FORECAST SOUNDINGS. AS LOW-LEVELS CONTINUE TO

MOISTEN AND WEAK ISENTROPIC ASCENT OCCURS COINCIDENT WITH

STRENGTHENING WARM NOSE NEAR 850 MB...THERMODYNAMIC PROFILES SHOULD

BECOME SUPPORTIVE OF FREEZING RAIN WITH TIME...WITH NEAR-SFC COLD

LAYER REINFORCED BY WET-BULB COOLING. CURRENT FORECAST SCENARIO IS

AN INITIAL P-TYPE OF SNOW /OCCASIONALLY MIXED WITH SLEET/

TRANSITIONING TO PREDOMINANTLY FREEZING RAIN.

..ROGERS.. 01/18/2011

ATTN...WFO...PHI...AKQ...LWX...RNK...

http://www.spc.noaa.gov/products/md/md0028.html

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