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Key Synoptic Features

Key Synoptic Features. Retreating shallow cold air mass SFC18z Broad SE surface flow along East Coast 55-65+kt 850mb over eastern Lakes 850W Weak surface circulation apparent near the Middle Atlantic Coast may interfere with low-level warm advection 4PANEL

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Key Synoptic Features

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  1. Key Synoptic Features • Retreating shallow cold air mass SFC18z • Broad SE surface flow along East Coast • 55-65+kt 850mb over eastern Lakes 850W • Weak surface circulation apparent near the Middle Atlantic Coast may interfere with low-level warm advection 4PANEL • Warm front/occluding cold front to the west likely to cross zones by end of period

  2. Additional Forecast Concerns • Affect of high terrain (White mountains reach 4000-6000 feet over N. Central New Hampshire TOPO • Stable air trapping chill in valleys statewide • Moist advection/cold surface = fog producer

  3. Verification Procedure • Eliminated “all-zero” categories • Easy: Dust(14),Smoke(16),Short-period flooding(22,23,24), Big Snow(5,6,7) Severe(27) -- No lightning on NLDN plot -- Used MWN to eliminate Wind Chill(18-19) • CHILL CHARTMWN OBS

  4. Verification Procedure • The search for snow: • Zone 3: KMWN 232258Z 18033G46KT 0SM -FZRAPLSN FZFG VV000 M02/M02 RMK SNB15FZRAPLB25 VRY LGT GICG= • Zone 4 : 1P1 reported snow alternating with UP much of the time from 20z to 5z…rejected based on sounding data with deep warm layer 0z MODEL SOUNDING • No other snow reports found…assumed only brief snow at highest elevations based on MWN • FLURRIES MAP (CAT 1)

  5. Verification Procedures • Finding Fog: -- Most ASOS reported visibility <=1/2 mile (exceptions:LEB,ASH, HIE) many reported 1/4 mile or lower. • All zones were judged to have verified based on extensive ASOS coverage combined with warm advection of cold, snow covered ground. Snow Cover • FOG MAP (CAT 17)

  6. Verification Procedures • Inferring Ice: • Observations of freezing rain/drizzle were found at all ASOS except PSM in Zone 14 (Zone1 had no ASOS to confirm icing • IP at MWN was brief and mixed • No station reported >0.24” while ice was the primary precip type • Scanned WSI PType graphics for added context. • only Zones 1(north), 14 (coast) were judged to have no icing • WSI_22zWSI_0ZWSI_2ZZR MAP

  7. Verification Procedures • What about wind: • MWN as usual gets blown away • No ASOS station reaches wind thresholds. • Check of mesonet data shows a couple of candidates but, they were rejected due to their isolated nature, strong low level stability and lack of support from higher quality data. SOUNDINGMESONET MAX WIND MAP

  8. Verification Procedures • Fishing for frost: • Support for three hours of freezing temps (cat 20) was found in all zones except 14 (coast based on 18-21UTC ASOS and mesonet data with primary support from NCEP hourly RTMA. RTMA freeze

  9. Verification Procedures • Defining the dampness: • NWS multi-sensor data combined with ground truth from ASOS and mesonet gauges was used to verify. • Only major question was accepting the validity of 1” amounts… accepted based on five gauges and NWS multi-sensor product MULTISENSORGAUGES

  10. Verification Procedures • Finding the forties: • ASOS and mesonet data showed trapped valley chill through the period. Late arriving precip allowed early warming in Zone 1 (north). RTMA did not capture the warming in Zone 1 shown in the data. RTMA used to help support valley chill farther south. RTMA 40F

  11. Verification summary • No zones verified for CAT 2-7,11,14,16,18-19, 22-27 • All zones verified for CAT 17 (DENSE FOG) • All zones except 14 (coast) verified for 3HR FREEZE • All zones except 1 and 14 verified for ZR…no ice storm • Only zone 2 (thanks to MWN) verified for WIND (12,13) • Only zone 2 (thanks to MWN) verified for ICE PELLETS • Only zone 2 (thanks to MWN) had flurries and blizzard • Zones 3,4 and 6 verified for 1” precip (CAT 21) • Northern and central zones had 0.5” precip (1-6, 8-9) • Trapped valley chill kept 40s out of zones 4,5,7-9

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