Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20261110_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 11/10 18Z 0.79 2422  94  62   0 0.00
Tue 11/10 21Z 1.26 2528  91  66   1 0.01
Wed 11/11 00Z 1.50 2828  91  76   0 0.03
Wed 11/11 03Z 1.37 2930  93  71  -1 0.04
Wed 11/11 06Z 1.15 3029  95  41  -3 0.01
Wed 11/11 09Z 0.87 3024  95  26  -4 0.00
Wed 11/11 12Z 0.72 3019  93  20  -5 0.00
Wed 11/11 15Z 0.72 2913  91  18  -5 0.01
Wed 11/11 18Z 1.22 2813  83  17  -4 0.00
Wed 11/11 21Z 0.98 2911  79  17  -3 0.00
Thu 11/12 00Z 0.42 2908  79  25  -3 0.00
Thu 11/12 03Z 0.17 2604  78  56  -3 0.00
Thu 11/12 06Z 0.07 2005  83  94  -2 0.00
Thu 11/12 09Z 0.03 1706  81  90  -1 0.00
Thu 11/12 12Z 0.10 1509  89  95  -1 0.01
Thu 11/12 15Z 0.19 1414  97  97  -1 0.08
Thu 11/12 18Z 0.25 1415  98  96  -1 0.09
Thu 11/12 21Z 0.33 1216  98  95  -1 0.08
Fri 11/13 00Z 0.33 1215  99  97   0 0.10
Fri 11/13 03Z 0.36 1114  99  96  -1 0.19
Fri 11/13 06Z 0.26 1010  99  96  -1 0.15
Fri 11/13 09Z 0.18 0806  99  97  -1 0.11
Fri 11/13 12Z 0.15 0507  99  96  -2 0.08
Fri 11/13 15Z 0.07 0206  99  96  -2 0.14

Run total areal avg QPF for the greens is: 1.13 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