NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20251120_0000
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)
=== ===== === ==== ==== === === === ====
Thu 11/20 00Z 0.13 3310  74  12  -5 0.00
Thu 11/20 03Z 0.04 3407  72  17  -3 0.00
Thu 11/20 06Z 0.04 3203  71  17  -3 0.00
Thu 11/20 09Z 0.08 2603  69  19  -3 0.00
Thu 11/20 12Z 0.12 2605  65  31  -2 0.00
Thu 11/20 15Z 0.10 2504  56  58  -2 0.00
Thu 11/20 18Z 0.09 2304  52  66  -1 0.00
Thu 11/20 21Z 0.05 2104  45  57  -1 0.00
Fri 11/21 00Z 0.06 2007  41  51   0 0.00
Fri 11/21 03Z 0.10 2011  38  55   0 0.00
Fri 11/21 06Z 0.16 2113  29  59   1 0.00
Fri 11/21 09Z 0.35 2417  58  54  -1 0.00
Fri 11/21 12Z 0.24 2215  68  53   0 0.00
Fri 11/21 15Z 0.35 2321  79  81   0 0.00
Fri 11/21 18Z 0.60 2523  98  45  -1 0.01
Fri 11/21 21Z 0.75 2528  96  11   0 0.02
Sat 11/22 00Z 1.02 2627  96   6  -2 0.01
Sat 11/22 03Z 1.03 2721  95   9  -4 0.01
Sat 11/22 06Z 0.85 2719  94  10  -5 0.00
Sat 11/22 09Z 0.62 2918  91  11  -7 0.00
Sat 11/22 12Z 0.51 3219  93  15  -9 0.00
Sat 11/22 15Z 0.66 3221  89  24 -10 0.00
Sat 11/22 18Z 1.29 3219  85  13  -9 0.00
Sat 11/22 21Z 0.63 3220  89  17  -9 0.00
Sun 11/23 00Z 0.54 3019  82   8  -8 0.00
Sun 11/23 03Z 0.43 3018  78   9  -7 0.00
Sun 11/23 06Z 0.47 2919  79  58  -7 0.00
Sun 11/23 09Z 0.52 2920  81  34  -7 0.00
Sun 11/23 12Z 0.56 2819  84  29  -8 0.00

Run total areal avg QPF for the greens is: 0.05 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