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Winter Weather Advisory in Effect for Eastern Vermont 7 PM Tonight Through 10 AM Friday

A Winter Weather Advisory is in effect from 7 PM tonight to 10 AM Friday for portions of eastern Vermont. Freezing rain is expected in these areas, especially above 1000 feet elevation. Slick travel conditions are possible, so be sure to slow down and use caution if traveling this evening into Friday morning. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260402_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 04/02 18Z 0.10 1509  95  70   0 0.00
Thu 04/02 19Z 0.14 1412  94  77   0 0.00
Thu 04/02 20Z 0.15 1414  94  83   0 0.00
Thu 04/02 21Z 0.15 1515  93  86   0 0.00
Thu 04/02 22Z 0.15 1517  94  96   0 0.00
Thu 04/02 23Z 0.15 1520  94  99   1 0.00
Fri 04/03 00Z 0.11 1623  96  98   1 0.02
Fri 04/03 02Z 0.05 1726  96  91   3 0.03
Fri 04/03 03Z 0.03 1728  97  90   3 0.02
Fri 04/03 04Z 0.03 1831  97  90   4 0.02
Fri 04/03 05Z 0.08 1833  97  89   5 0.05
Fri 04/03 06Z 0.12 1933  97  81   7 0.05
Fri 04/03 07Z 0.18 2034  97  72   8 0.04
Fri 04/03 08Z 0.21 2034  96  71   9 0.03
Fri 04/03 09Z 0.24 2036  96  84  10 0.03
Fri 04/03 10Z 0.30 2139  96  87  10 0.03
Fri 04/03 11Z 0.34 2140  95  89  11 0.03
Fri 04/03 12Z 0.40 2241  97  88  11 0.03
Fri 04/03 13Z 0.43 2239  96  91  11 0.05
Fri 04/03 14Z 0.47 2239  98  90  11 0.04
Fri 04/03 15Z 0.54 2339  96  89  11 0.05
Fri 04/03 16Z 0.60 2439  94  75  11 0.03
Fri 04/03 17Z 0.65 2438  95  81  11 0.01
Fri 04/03 18Z 0.71 2438  95  78  11 0.01
Fri 04/03 19Z 0.76 2538  95  78  11 0.01
Fri 04/03 20Z 0.83 2538  95  46  11 0.01
Fri 04/03 21Z 0.95 2538  94  42  10 0.00
Fri 04/03 22Z 1.05 2539  93  47  10 0.00
Fri 04/03 23Z 1.11 2541  94  31  10 0.00
Sat 04/04 00Z 1.21 2541  96  20   9 0.00
Sat 04/04 01Z 1.34 2543  95  13   9 0.01
Sat 04/04 02Z 1.34 2641  92  11   8 0.02
Sat 04/04 03Z 1.31 2640  93  10   7 0.02
Sat 04/04 04Z 1.11 2737  90  12   6 0.02
Sat 04/04 05Z 0.92 2735  87  21   5 0.03
Sat 04/04 06Z 0.74 2833  85  34   4 0.02
Sat 04/04 07Z 0.57 2929  85  26   3 0.01
Sat 04/04 08Z 0.43 3025  87  19   2 0.01
Sat 04/04 09Z 0.31 3122  89  23   2 0.01
Sat 04/04 10Z 0.19 3218  89  21   1 0.01
Sat 04/04 11Z 0.13 3415  89  24   1 0.01
Sat 04/04 12Z 0.10 3512  90  24   1 0.01
Sat 04/04 13Z 0.10 0109  89  28   1 0.00
Sat 04/04 14Z 0.12 0407  88  30   2 0.00
Sat 04/04 15Z 0.14 0806  88  43   2 0.00
Sat 04/04 16Z 0.15 1107  90  38   1 0.00
Sat 04/04 17Z 0.16 1309  89  40   2 0.00
Sat 04/04 18Z 0.17 1412  88  53   2 0.00
Sat 04/04 19Z 0.19 1515  87  49   2 0.00
Sat 04/04 20Z 0.23 1518  86  39   2 0.00
Sat 04/04 21Z 0.22 1520  86  39   3 0.00
Sat 04/04 22Z 0.15 1622  82  78   4 0.00
Sat 04/04 23Z 0.11 1625  80  97   5 0.00
Sun 04/05 00Z 0.08 1727  83  95   6 0.01
Sun 04/05 01Z 0.08 1730  84  94   6 0.01
Sun 04/05 02Z 0.06 1732  87  93   7 0.00
Sun 04/05 03Z 0.06 1734  89  82   8 0.00
Sun 04/05 04Z 0.05 1836  92  86   8 0.00
Sun 04/05 05Z 0.05 1838  94  88   9 0.01

Run total areal avg QPF for the greens is: 0.80 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1