WINTER WEATHER FORECASTING IN THE SOUTHEAST
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WINTER WEATHER FORECASTING IN THE SOUTHEAST. BACKGROUND RESEARCH. Collaborative Science, Technology, and Applied Research (CSTAR) Project *NWS Offices *NC State University *NC State Climate Office

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BACKGROUND RESEARCH

Collaborative Science, Technology, and Applied Research (CSTAR) Project *NWS Offices *NC State University *NC State Climate Office

Evaluation of the Real-Time MM5 Modeling System *NC State University *NC State Climate Office *Capitol Broadcasting *NCSC/MCNC

SPECIAL THANKS TO DR. GARY LACKMANN FOR PERMISSION TO USE SEVERAL VALUABLE POWERPOINT SLIDES


FORECASTING CHALLENGES

  • Cold Air Damming

  • Coastal Low Pressures

  • Precipitation Type


BUILDING HIGH PRESSURE

CONFLUENCE ALOFT 

SURFACE DIVERGENCE &PRESSURE RISES


E-W Elongated High

Confluence with little or no ridging at 500mb

Cold front just off-shore

DIABATICALLY ENHANCED CLASSICAL

(SYNOPTIC FORCING)


N-S Elongated High

Confluence with more ridging at 500mb

Cold front far off-shore

DRY ONSET CLASSICAL

(SYNOPTIC FORCING)


HYBRID CAD

Equal synoptic/diabatic processes

Weak and progressive high

IN-SITU CAD

Diabatic processes prevail

High in unfavorable location

Little or no CAA


WHATDO YOULOOK FOR?

High Pressure ~1030mb in New England

U-shaped Isobars east of Appalachians

546 line- Mix540 line- Snow

Timing of Precip (am/pm)

Surface Plot

CONTAINS: * Mean Sea Level Pressure Isobars (mb) * 6-hour Total Precipitation (in) * 1000-500 mb Thickness (dm)


WHATDO YOULOOK FOR?

Southerly to easterly winds

Temperatures < 0C Snow< 3C Mix

Warm Air Intrusion

850 mb Plot

CONTAINS: * 850 mb Height (dm) * 850 mb Temperature (C) * 850 mb Winds (kts)


WHATDO YOULOOK FOR?

Relative Humidity >70%

Negative Omegas Co-located with RH

Dry Air Intrusion

Westerly Winds

700 mb Plot

CONTAINS: * 700 mb Heights (dm) * Relative Humidity (%) * Omega (mb/s)


WHATDO YOULOOK FOR?

Southwest Winds

Tilt of 500 mb Trough

Confluent Flow over New England

500 mb Plot

CONTAINS: * 500 mb Heights (dm) * Absolute Vorticity (s^-1) * 500 mb Winds (kts)


WHATDO YOULOOK FOR?

Confluent Flow over New England

Jet stream and streaks

Split Flow/ Dual Jet Structure

300 mb Plot

CONTAINS: * 300 mb Heights (dm) * 300 mb Isotachs (kts) * 300 mb Winds (kts)


PRECIPITATION TYPE FORECASTING

FEBRUARY 5-6, 2004

Potential SC Ice Storm/CAD Event

(1)What is p-type?

(2)How do we make an educated guess?

(3)PUTTING THE METHOD TO USE…


COLD AIR DAMMING&WINTER PRECIPITATION TYPES

(1)

32 F

0C

WARM NOSE

(2)

Warm, moist air

COLD, DRY AIR

(3)

Rain Freezing Rain Sleet Snow

SOUTH

NORTH


PARTIAL THICKNESS AND GENERAL FORECASTING RULES

Partial thickness - the distance between intermediate levels in the atmosphere found in the model output, typically between 1000 and 500 millibars (i.e. 1000-850, 850-700, 700-500) that represent the thermal structure in the atmosphere with increasing height

TO DO ON-THE-FLY FORECASTING:

For snow to fall:

1000-850 THK < 1290m 850-700 THK < 1540m

For sleet/freezing rain to fall:

850-700 THK 1540-1555m Sleet > 1555m Freezing Rain

(larger values of the 850-700 THK indicate warmer air aloft)


1000-500 THK

&

850 HEIGHT

1575

5540

????????????????

WILL IT BE……

SNOW, SLEET, ORFREEZING RAIN

????????????????

Surface

850 mb

700 HEIGHT

&

500 HEIGHT

3160

5790

700 mb

500 mb


500mb 5790m

700mb 3160m

700-500 THK 2630m

700mb 3160m

850mb 1575m

850-700 THK 1585m

1000-500 THK 5540m

700-500 THK 2630m

850-700 THK 1585m

1000-850 THK 1325m

So for the Columbia Area in the Event from Thursday, Feb. 5th…

>1540m => no snow, warm nose present

>1300m => too warm to freeze


P-TYPE FORECASTING NOMOGRAM

1325/1585

RAIN

1000-850mb THK

850-700mb THK



Related/Future Research

CAD Erosion (Stanton 2003, MS Thesis, NCSU)

High-resolution modeling (Caldwell 2004, MS Thesis, NCSU)

Coastal Frontogenesis (Appel 2002, MS Thesis, NCSU)

Quantitative Precipitation Forecasting (QPF)


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