Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260301_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 03/01 12Z 0.19 3213 87 88 -12 0.00
Sun 03/01 13Z 0.17 3217 85 72 -13 0.00
Sun 03/01 14Z 0.20 3217 77 53 -13 0.00
Sun 03/01 15Z 0.29 3118 73 43 -13 0.00
Sun 03/01 16Z 0.32 3120 72 42 -14 0.00
Sun 03/01 17Z 0.34 3120 70 30 -15 0.00
Sun 03/01 19Z 0.50 3119 70 30 -16 0.00
Sun 03/01 20Z 0.51 3119 74 38 -17 0.00
Sun 03/01 21Z 0.53 3119 77 47 -17 0.00
Sun 03/01 22Z 0.54 3119 80 53 -17 0.00
Sun 03/01 23Z 0.53 3020 78 59 -18 0.00
Mon 03/02 00Z 0.54 3021 74 53 -19 0.00
Mon 03/02 01Z 0.47 3122 65 41 -19 0.00
Mon 03/02 02Z 0.37 3122 55 29 -19 0.00
Mon 03/02 03Z 0.31 3121 49 21 -19 0.00
Mon 03/02 04Z 0.28 3121 47 16 -19 0.00
Mon 03/02 05Z 0.27 3120 46 12 -19 0.00
Mon 03/02 06Z 0.26 3119 44 9 -19 0.00
Mon 03/02 07Z 0.26 3119 42 7 -19 0.00
Mon 03/02 08Z 0.27 3119 40 6 -19 0.00
Mon 03/02 09Z 0.28 3119 41 7 -19 0.00
Mon 03/02 10Z 0.28 3018 42 8 -19 0.00
Mon 03/02 11Z 0.31 3019 47 9 -19 0.00
Mon 03/02 13Z 0.36 2920 55 18 -19 0.00
Mon 03/02 14Z 0.36 2919 55 18 -19 0.00
Mon 03/02 15Z 0.37 2918 52 19 -19 0.00
Mon 03/02 16Z 0.40 2917 46 19 -18 0.00
Mon 03/02 17Z 0.41 2917 40 17 -18 0.00
Mon 03/02 18Z 0.38 2916 39 14 -17 0.00
Mon 03/02 19Z 0.36 2914 41 14 -16 0.00
Mon 03/02 20Z 0.32 2912 41 12 -15 0.00
Mon 03/02 21Z 0.32 2812 41 9 -14 0.00
Mon 03/02 22Z 0.32 2712 42 15 -13 0.00
Mon 03/02 23Z 0.33 2613 42 33 -13 0.00
Tue 03/03 00Z 0.35 2515 43 50 -12 0.00
Tue 03/03 01Z 0.40 2418 39 50 -11 0.00
Tue 03/03 02Z 0.45 2422 33 62 -10 0.00
Tue 03/03 03Z 0.51 2425 26 58 -9 0.00
Tue 03/03 04Z 0.56 2528 29 57 -8 0.00
Tue 03/03 05Z 0.57 2529 29 55 -7 0.00
Tue 03/03 06Z 0.57 2530 27 55 -6 0.00
Tue 03/03 07Z 0.55 2529 29 55 -5 0.00
Tue 03/03 08Z 0.53 2527 29 53 -4 0.00
Tue 03/03 09Z 0.50 2526 30 50 -4 0.00
Tue 03/03 10Z 0.50 2526 30 46 -4 0.00
Tue 03/03 11Z 0.50 2426 30 42 -3 0.00
Tue 03/03 12Z 0.48 2425 29 37 -3 0.00
Tue 03/03 13Z 0.45 2424 34 29 -3 0.00
Tue 03/03 14Z 0.43 2424 40 23 -2 0.00
Tue 03/03 15Z 0.44 2325 49 16 -2 0.00
Tue 03/03 16Z 0.46 2326 61 14 -2 0.00
Tue 03/03 17Z 0.48 2326 77 12 -2 0.00
Tue 03/03 18Z 0.51 2327 88 13 -3 0.00
Tue 03/03 19Z 0.52 2326 93 17 -3 0.00
Tue 03/03 20Z 0.51 2326 95 34 -3 0.01
Tue 03/03 21Z 0.46 2324 96 38 -2 0.01
Tue 03/03 22Z 0.40 2321 96 61 -1 0.01
Tue 03/03 23Z 0.36 2320 96 91 0 0.01
Run total areal avg QPF for the Central_Greens is: 0.04 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