Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260629_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)
=== ===== === ==== ==== === === === ====
Mon 06/29 12Z 0.06 3512  76  43  13 0.00
Mon 06/29 15Z 0.14 3509  76  46  13 0.00
Mon 06/29 18Z 0.63 3407  67  36  13 0.00
Mon 06/29 21Z 0.88 3207  58  23  14 0.00
Tue 06/30 00Z 0.17 3307  49  25  14 0.00
Tue 06/30 03Z 0.28 3004  49  20  14 0.00
Tue 06/30 06Z 0.51 2707  57  32  14 0.00
Tue 06/30 09Z 0.67 2709  61  34  14 0.00
Tue 06/30 12Z 0.42 2508  68  61  14 0.00
Tue 06/30 15Z 0.44 2310  68  61  15 0.00
Tue 06/30 18Z 0.47 2114  68  77  15 0.00
Tue 06/30 21Z 0.67 2118  85  93  16 0.03
Wed 07/01 00Z 1.03 2326  88  67  17 0.05
Wed 07/01 03Z 1.33 2536  87  42  18 0.00
Wed 07/01 06Z 1.18 2839  91  54  19 0.02
Wed 07/01 09Z 0.89 2931  97  18  19 0.01
Wed 07/01 12Z 0.63 2922  94  28  18 0.01
Wed 07/01 15Z 0.54 3018  91  15  19 0.00
Wed 07/01 18Z 0.37 2810  78  47  21 0.00
Wed 07/01 21Z 0.56 2711  78  73  21 0.00
Thu 07/02 00Z 0.55 2713  91  53  20 0.14
Thu 07/02 03Z 0.87 2817  84  31  20 0.02
Thu 07/02 06Z 0.69 2818  87  40  20 0.00
Thu 07/02 09Z 0.68 2816  87  41  20 0.00
Thu 07/02 12Z 0.65 2817  92  50  20 0.01
Thu 07/02 15Z 0.68 2816  84  28  20 0.03
Thu 07/02 18Z 2.92 2517  78  39  20 0.00
Thu 07/02 21Z 4.98 2618  56  54  21 0.00
Fri 07/03 00Z 1.81 2530  59  31  21 0.00

Run total areal avg QPF for the greens is: 0.32 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