BACKGROUND RESEARCH FORECASTING CHALLENGES (1)Cold Air Damming (2)Coastal Low Pressures (3)Precipitation Type.

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Presentation transcript:

BACKGROUND RESEARCH

FORECASTING CHALLENGES (1)Cold Air Damming (2)Coastal Low Pressures (3)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

Surface Plot CONTAINS: * Mean Sea Level Pressure Isobars (mb) * 6-hour Total Precipitation (in) * mb Thickness (dm) WHAT DO YOU LOOK FOR? High Pressure ~1030mb in New England U-shaped Isobars east of Appalachians 546 line- Mix 540 line- Snow Timing of Precip (am/pm)

850 mb Plot CONTAINS: * 850 mb Height (dm) * 850 mb Temperature (C) * 850 mb Winds (kts) WHAT DO YOU LOOK FOR? Southerly to easterly winds Temperatures < 0C Snow < 3C Mix Warm Air Intrusion

700 mb Plot CONTAINS: * 700 mb Heights (dm) * Relative Humidity (%) * Omega (mb/s) WHAT DO YOU LOOK FOR? Relative Humidity >70% Negative Omegas Co- located with RH Dry Air Intrusion Westerly Winds

500 mb Plot WHAT DO YOU LOOK FOR? Southwest Winds Tilt of 500 mb Trough Confluent Flow over New England CONTAINS: * 500 mb Heights (dm) * Absolute Vorticity (s^-1) * 500 mb Winds (kts)

300 mb Plot WHAT DO YOU LOOK FOR? Confluent Flow over New England Jet stream and streaks Split Flow/ Dual Jet Structure 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…

32 F0C COLD AIR DAMMING & WINTER PRECIPITATION TYPES Warm, moist air COLD, DRY AIR Rain Freezing Rain Sleet Snow WARM NOSE NORTH SOUTH (1) (2) (3)

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 , , ) that represent the thermal structure in the atmosphere with increasing height TO DO ON-THE-FLY FORECASTING: For snow to fall: THK < 1290m THK < 1540m For sleet/freezing rain to fall: THK mSleet > 1555mFreezing Rain (larger values of the THK indicate warmer air aloft)

Surface850 mb 700 mb500 mb THK & 850 HEIGHT 700 HEIGHT & 500 HEIGHT ???????????????? WILL IT BE…… SNOW, SLEET, OR FREEZING RAIN ????????????????

So for the Columbia Area in the Event from Thursday, Feb. 5th… 500mb5790m 700mb3160m THK2630m 700mb3160m 850mb1575m THK1585m THK5540m THK2630m THK1585m THK1325m >1540m => no snow, warm nose present >1300m => too warm to freeze

P-TYPE FORECASTING NOMOGRAM 1325/ mb THK mb THK RAIN

Actual Observations

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)