NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20251114_0000
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)
=== ===== === ==== ==== === === === ====
Fri 11/14 00Z 0.82 3021  97  80  -7 0.00
Fri 11/14 03Z 0.75 3122  92  76  -7 0.00
Fri 11/14 06Z 0.69 3122  94  75  -8 0.00
Fri 11/14 09Z 0.64 3222  95  69  -8 0.01
Fri 11/14 12Z 0.58 3221  95  56  -9 0.00
Fri 11/14 15Z 0.50 3218  94  60  -9 0.00
Fri 11/14 18Z 1.10 3116  92  71  -9 0.00
Fri 11/14 21Z 0.69 3117  88  82  -8 0.00
Sat 11/15 00Z 0.59 3221  87  81  -9 0.00
Sat 11/15 03Z 0.38 3319  89  49  -9 0.00
Sat 11/15 06Z 0.37 3317  91  34  -9 0.00
Sat 11/15 09Z 0.37 3217  87  24  -9 0.00
Sat 11/15 12Z 0.26 3115  79  13  -7 0.00
Sat 11/15 15Z 0.19 3010  66   7  -4 0.00
Sat 11/15 18Z 0.26 2712  52  86  -2 0.00
Sat 11/15 21Z 0.20 2511  46  90   1 0.00
Sun 11/16 00Z 0.11 2016  90  98   2 0.03
Sun 11/16 03Z 0.25 2125  98  97   4 0.31
Sun 11/16 06Z 0.29 2222  98  97   6 0.18
Sun 11/16 09Z 0.63 2627  96  94   3 0.28
Sun 11/16 12Z 1.42 2732  97  74  -1 0.09
Sun 11/16 15Z 2.10 2829  94  83  -5 0.03
Sun 11/16 18Z 2.04 2831  93  96  -6 0.03
Sun 11/16 21Z 1.68 2830  94  84  -4 0.04
Mon 11/17 00Z 2.06 2938  89  86  -9 0.03
Mon 11/17 03Z 1.77 2937  90  85  -9 0.04
Mon 11/17 06Z 1.48 2937  91  85 -10 0.05
Mon 11/17 09Z 1.25 3036  92  79 -10 0.03
Mon 11/17 12Z 0.94 3034  91  69  -9 0.03

Run total areal avg QPF for the greens is: 1.18 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