NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260929_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 09/29 06Z 0.02 0008  98  94   8 0.00
Tue 09/29 09Z 0.05 3513  97  82   9 0.02
Tue 09/29 12Z 0.04 3515  97  66   8 0.00
Tue 09/29 15Z 0.03 3515  97  67   8 0.00
Tue 09/29 18Z 0.04 3512  95  69   8 0.00
Tue 09/29 21Z 0.03 3513  93  63   9 0.00
Wed 09/30 00Z 0.03 0012  93  52   9 0.00
Wed 09/30 03Z 0.04 0108  93  36   9 0.00
Wed 09/30 06Z 0.04 3504  92  29   9 0.00
Wed 09/30 09Z 0.04 3406  84  26  10 0.00
Wed 09/30 12Z 0.03 3405  76  19  11 0.00
Wed 09/30 15Z 0.08 3105  69  18  12 0.00
Wed 09/30 18Z 0.12 2705  63  17  12 0.00
Wed 09/30 21Z 0.22 2708  66  19  11 0.00
Thu 10/01 00Z 0.34 2711  74  25  11 0.00
Thu 10/01 03Z 0.49 2614  79  52  11 0.00
Thu 10/01 06Z 0.72 2619  84  61  10 0.00
Thu 10/01 09Z 0.75 2524  88  90  10 0.02
Thu 10/01 12Z 0.62 2721  86  80  11 0.02
Thu 10/01 15Z 0.57 2618  84  91  11 0.01
Thu 10/01 18Z 0.60 2318  71  88  12 0.00
Thu 10/01 21Z 0.73 2324  80  95  11 0.00
Fri 10/02 00Z 0.81 2529  99  97  11 0.04
Fri 10/02 03Z 0.72 2423  83  93  11 0.02
Fri 10/02 06Z 0.73 2823  96  33  11 0.02
Fri 10/02 09Z 0.58 2818  90  29  11 0.00
Fri 10/02 12Z 0.42 2715  83  52  12 0.00
Fri 10/02 15Z 0.36 2514  74  90  12 0.01
Fri 10/02 18Z 0.45 2413  91  81  11 0.00

Run total areal avg QPF for the greens is: 0.16 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