NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260509_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 05/09 06Z 1.05 2513  60  45   0 0.00
Sat 05/09 09Z 0.73 2611  47  40   0 0.00
Sat 05/09 12Z 0.24 2011  52  44   0 0.00
Sat 05/09 15Z 0.99 1614  72  59   1 0.00
Sat 05/09 18Z 1.21 1520  85  74   1 0.06
Sat 05/09 21Z 0.12 1622  95  81   2 0.05
Sun 05/10 00Z 0.07 1824  96  74   4 0.02
Sun 05/10 03Z 0.24 1923  96  21   3 0.00
Sun 05/10 06Z 0.41 2125  91  29   4 0.00
Sun 05/10 09Z 0.75 2331  91  89   5 0.01
Sun 05/10 12Z 1.06 2625  94  59   2 0.03
Sun 05/10 15Z 13.23 2518  69   8   1 0.00
Sun 05/10 18Z 13.59 2519  46  21   2 0.00
Sun 05/10 21Z 14.79 2521  46  29   2 0.00
Mon 05/11 00Z 3.54 2621  48  26   0 0.00
Mon 05/11 03Z 1.53 2822  64  34  -1 0.00
Mon 05/11 06Z 1.04 2920  62  38  -2 0.00
Mon 05/11 09Z 0.92 2915  57  37  -2 0.00
Mon 05/11 12Z 0.56 2811  47  53  -2 0.00
Mon 05/11 15Z 5.40 2810  50  65  -2 0.00
Mon 05/11 18Z 8.56 2612  55  70  -1 0.00
Mon 05/11 21Z 6.18 2811  56  69   0 0.00
Tue 05/12 00Z 2.81 3214  64  72  -1 0.00
Tue 05/12 03Z 5.25 2911  58  70  -1 0.00
Tue 05/12 06Z 0.76 3417  62  25  -3 0.00
Tue 05/12 09Z 0.20 3517  62  33  -3 0.00
Tue 05/12 12Z 0.20 3415  65  16  -4 0.00
Tue 05/12 15Z 3.73 3211  65   9  -4 0.00
Tue 05/12 18Z 5.64 3112  61  13  -3 0.00

Run total areal avg QPF for the greens is: 0.17 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