Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20261027_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)
=== ===== === ==== ==== === === === ====
Tue 10/27 06Z 0.17 3419  70   6  -2 0.00
Tue 10/27 09Z 0.09 3415  60   5  -2 0.00
Tue 10/27 12Z 0.05 3413  51   7  -1 0.00
Tue 10/27 15Z 0.08 3309  51   7  -1 0.00
Tue 10/27 18Z 0.13 3208  46   5  -1 0.00
Tue 10/27 21Z 0.16 3108  40   3   0 0.00
Wed 10/28 00Z 0.15 3108  40   7   0 0.00
Wed 10/28 03Z 0.08 3205  37   6   0 0.00
Wed 10/28 06Z 0.07 2803  30   5   0 0.00
Wed 10/28 09Z 0.11 2505  26  30   1 0.00
Wed 10/28 12Z 0.15 2507  24  58   2 0.00
Wed 10/28 15Z 0.18 2509  26  86   3 0.00
Wed 10/28 18Z 0.19 2609  33  82   5 0.00
Wed 10/28 21Z 0.22 2510  42  93   6 0.00
Thu 10/29 00Z 0.29 2413  53  83   6 0.00
Thu 10/29 03Z 0.40 2416  68  51   6 0.00
Thu 10/29 06Z 0.43 2516  81  29   6 0.00
Thu 10/29 09Z 0.45 2516  86  29   6 0.00
Thu 10/29 12Z 0.51 2519  89  39   6 0.00
Thu 10/29 15Z 0.49 2419  84  40   6 0.00
Thu 10/29 18Z 0.56 2418  80  30   7 0.00
Thu 10/29 21Z 0.89 2426  77  27   7 0.00
Fri 10/30 00Z 1.09 2433  76  86   8 0.00
Fri 10/30 03Z 1.15 2634  89  88   7 0.02

Run total areal avg QPF for the greens is: 0.02 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