Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260301_1200
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)
=== ===== === ==== ==== === === === ====
Sun 03/01 12Z 0.26 3214 85 86 -13 0.00
Sun 03/01 13Z 0.27 3217 83 67 -13 0.00
Sun 03/01 14Z 0.29 3117 76 43 -14 0.00
Sun 03/01 15Z 0.38 3118 75 37 -15 0.00
Sun 03/01 16Z 0.42 3119 75 34 -15 0.00
Sun 03/01 17Z 0.47 3120 73 26 -16 0.00
Sun 03/01 19Z 0.63 3119 74 28 -17 0.00
Sun 03/01 20Z 0.67 3120 76 36 -18 0.00
Sun 03/01 21Z 0.69 3020 76 43 -18 0.00
Sun 03/01 22Z 0.67 3021 75 46 -18 0.00
Sun 03/01 23Z 0.64 3022 73 49 -19 0.00
Mon 03/02 00Z 0.63 3022 70 43 -19 0.00
Mon 03/02 01Z 0.57 3023 63 34 -20 0.00
Mon 03/02 02Z 0.47 3122 55 25 -20 0.00
Mon 03/02 03Z 0.40 3121 50 20 -20 0.00
Mon 03/02 04Z 0.37 3121 48 17 -20 0.00
Mon 03/02 05Z 0.36 3120 45 14 -20 0.00
Mon 03/02 06Z 0.34 3119 43 12 -20 0.00
Mon 03/02 07Z 0.34 3019 42 10 -20 0.00
Mon 03/02 08Z 0.35 3019 40 9 -20 0.00
Mon 03/02 09Z 0.35 3019 41 9 -20 0.00
Mon 03/02 10Z 0.36 3019 42 10 -20 0.00
Mon 03/02 11Z 0.37 3019 45 11 -20 0.00
Mon 03/02 13Z 0.41 2920 51 17 -20 0.00
Mon 03/02 14Z 0.41 2919 51 19 -20 0.00
Mon 03/02 15Z 0.41 2918 50 20 -19 0.00
Mon 03/02 16Z 0.44 2917 45 21 -19 0.00
Mon 03/02 17Z 0.46 2917 41 19 -18 0.00
Mon 03/02 18Z 0.44 2916 40 17 -18 0.00
Mon 03/02 19Z 0.42 2815 41 16 -17 0.00
Mon 03/02 20Z 0.38 2813 41 13 -16 0.00
Mon 03/02 21Z 0.38 2713 40 10 -15 0.00
Mon 03/02 22Z 0.38 2714 40 13 -14 0.00
Mon 03/02 23Z 0.38 2615 40 28 -13 0.00
Tue 03/03 00Z 0.37 2516 40 53 -12 0.00
Tue 03/03 01Z 0.39 2419 37 60 -11 0.00
Tue 03/03 02Z 0.44 2422 34 70 -10 0.00
Tue 03/03 03Z 0.51 2425 29 67 -10 0.00
Tue 03/03 04Z 0.56 2428 27 66 -9 0.00
Tue 03/03 05Z 0.60 2530 25 65 -8 0.00
Tue 03/03 06Z 0.61 2530 22 65 -7 0.00
Tue 03/03 07Z 0.60 2530 23 64 -6 0.00
Tue 03/03 08Z 0.58 2528 24 62 -5 0.00
Tue 03/03 09Z 0.56 2527 24 59 -5 0.00
Tue 03/03 10Z 0.56 2527 25 54 -4 0.00
Tue 03/03 11Z 0.56 2526 25 51 -4 0.00
Tue 03/03 12Z 0.53 2525 25 44 -4 0.00
Tue 03/03 13Z 0.49 2524 28 38 -4 0.00
Tue 03/03 14Z 0.44 2423 32 31 -3 0.00
Tue 03/03 15Z 0.43 2423 39 24 -3 0.00
Tue 03/03 16Z 0.42 2324 48 19 -3 0.00
Tue 03/03 17Z 0.42 2324 60 15 -3 0.00
Tue 03/03 18Z 0.43 2324 71 15 -3 0.00
Tue 03/03 19Z 0.42 2323 77 16 -3 0.00
Tue 03/03 20Z 0.40 2322 81 28 -2 0.00
Tue 03/03 21Z 0.36 2320 82 33 -2 0.00
Tue 03/03 22Z 0.32 2318 84 51 -1 0.01
Tue 03/03 23Z 0.28 2317 85 75 -1 0.01
Run total areal avg QPF for the greens is: 0.02 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