NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20250524_0600
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)
=== ===== === ==== ==== === === === ====
Sat 05/24 06Z 0.26 2907  98  96   0 0.00
Sat 05/24 09Z 0.23 3108  98  94   0 0.04
Sat 05/24 12Z 0.28 3111  98  93   0 0.03
Sat 05/24 15Z 0.39 3113  97  88  -1 0.01
Sat 05/24 18Z 0.48 3115  96  93  -1 0.00
Sat 05/24 21Z 0.44 3216  97  95   0 0.02
Sun 05/25 00Z 0.43 3217  98  92   0 0.02
Sun 05/25 03Z 0.42 3217  98  92   0 0.03
Sun 05/25 06Z 0.38 3320  97  90   0 0.03
Sun 05/25 09Z 0.31 3320  97  77  -1 0.01
Sun 05/25 12Z 0.27 3418  97  69  -2 0.01
Sun 05/25 15Z 0.25 3416  96  70  -1 0.00
Sun 05/25 18Z 1.73 3315  89  68   0 0.00
Sun 05/25 21Z 1.64 3415  84  83   1 0.00
Mon 05/26 00Z 0.12 3514  80  90   1 0.00
Mon 05/26 03Z 0.33 3312  79  96   2 0.00
Mon 05/26 06Z 0.38 3214  86  97   2 0.03
Mon 05/26 09Z 0.17 3415  87  90   2 0.02
Mon 05/26 12Z 0.04 3513  76  66   3 0.00
Mon 05/26 15Z 0.14 3509  77  51   3 0.00
Mon 05/26 18Z 2.01 3308  76  45   4 0.00
Mon 05/26 21Z 3.77 3210  69  29   5 0.00
Tue 05/27 00Z 0.42 3213  60  18   5 0.00
Tue 05/27 03Z 0.68 3310  68  31   5 0.00
Tue 05/27 06Z 0.37 3212  62  34   6 0.00
Tue 05/27 09Z 0.33 3212  56  39   6 0.00
Tue 05/27 12Z 0.44 3112  54  49   6 0.00
Tue 05/27 15Z 0.77 3009  57  54   6 0.00
Tue 05/27 18Z 3.27 3007  58  46   7 0.00

Run total areal avg QPF for the greens is: 0.25 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