NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260602_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)
=== ===== === ==== ==== === === === ====
Tue 06/02 18Z 4.44 3313  49  38   7 0.00
Tue 06/02 21Z 3.69 3317  48  31   8 0.00
Wed 06/03 00Z 0.30 3420  48  43   8 0.00
Wed 06/03 03Z 0.16 3517  47  41   9 0.00
Wed 06/03 06Z 0.10 0011  45  29   9 0.00
Wed 06/03 09Z 0.11 3406  43  15   9 0.00
Wed 06/03 12Z 0.36 3209  43  20   9 0.00
Wed 06/03 15Z 0.65 3112  46  35   9 0.00
Wed 06/03 18Z 3.35 3009  52  49  10 0.00
Wed 06/03 21Z 2.26 2809  54  52  11 0.00
Thu 06/04 00Z 0.73 2812  56  50  12 0.00
Thu 06/04 03Z 0.76 2913  57  40  12 0.00
Thu 06/04 06Z 0.42 3010  54  35  12 0.00
Thu 06/04 09Z 0.39 2908  47  31  12 0.00
Thu 06/04 12Z 0.56 2711  48  33  12 0.00
Thu 06/04 15Z 0.69 2714  57  32  12 0.00
Thu 06/04 18Z 4.12 2613  53  29  12 0.00
Thu 06/04 21Z 9.33 2715  55  30  12 0.00
Fri 06/05 00Z 2.25 2821  64  26  12 0.00
Fri 06/05 03Z 1.09 2925  69  24  11 0.00
Fri 06/05 06Z 0.99 3123  73  25  11 0.00
Fri 06/05 09Z 0.84 3119  67  14  10 0.00
Fri 06/05 12Z 0.79 2916  64   3  10 0.00
Fri 06/05 15Z 0.85 3019  68  14  10 0.00
Fri 06/05 18Z 8.18 2712  76  17  11 0.00
Fri 06/05 21Z 4.01 2611  73  61  12 0.00
Sat 06/06 00Z 1.28 2614  74  84  12 0.00
Sat 06/06 03Z 1.50 2718  74  94  12 0.00
Sat 06/06 06Z 0.99 2517  77  68  12 0.00

Run total areal avg QPF for the greens is: 0.00 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