NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260726_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)
=== ===== === ==== ==== === === === ====
Sun 07/26 12Z 0.12 2203  79  12  12 0.00
Sun 07/26 15Z 0.05 1704  80   8  13 0.00
Sun 07/26 18Z 0.33 1705  80  13  13 0.00
Sun 07/26 21Z 0.34 1806  81  31  13 0.00
Mon 07/27 00Z 0.18 2007  84  47  13 0.01
Mon 07/27 03Z 0.22 2107  80  56  13 0.00
Mon 07/27 06Z 0.25 2208  77  61  13 0.00
Mon 07/27 09Z 0.23 2306  85  76  13 0.01
Mon 07/27 12Z 0.20 2306  88  81  12 0.00
Mon 07/27 15Z 0.19 2205  90  80  12 0.03
Mon 07/27 18Z 0.45 2105  85  65  13 0.01
Mon 07/27 21Z 1.81 2605  84  82  14 0.01
Tue 07/28 00Z 0.41 2806  84  88  13 0.06
Tue 07/28 03Z 0.12 2104  81  84  13 0.01
Tue 07/28 06Z 0.27 2208  82  80  13 0.00
Tue 07/28 09Z 0.25 2209  84  75  13 0.00
Tue 07/28 12Z 0.14 2008  86  78  13 0.00
Tue 07/28 15Z 0.02 1709  89  83  13 0.03
Tue 07/28 18Z 0.04 1712  91  82  13 0.10
Tue 07/28 21Z 0.06 1712  90  85  13 0.07
Wed 07/29 00Z 0.10 1614  93  89  12 0.05
Wed 07/29 03Z 0.09 1614  94  86  13 0.02
Wed 07/29 06Z 0.13 1912  98  88  12 0.05
Wed 07/29 09Z 0.06 1713  95  88  12 0.10
Wed 07/29 12Z 0.14 1620  98  96  12 0.06
Wed 07/29 15Z 0.27 1624  96  98  11 0.13
Wed 07/29 18Z 0.39 1422  97  96  11 0.12
Wed 07/29 21Z 0.50 1219  95  94  10 0.04
Thu 07/30 00Z 0.53 1120  92  97  10 0.03

Run total areal avg QPF for the greens is: 0.94 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