NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20251226_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)
=== ===== === ==== ==== === === === ====
Fri 12/26 06Z 0.13 3428  73   7 -15 0.00
Fri 12/26 07Z 0.10 3431  65   5 -15 0.00
Fri 12/26 08Z 0.08 3530  62   5 -15 0.00
Fri 12/26 09Z 0.04 3529  58   5 -15 0.00
Fri 12/26 10Z 0.02 0027  52   5 -14 0.00
Fri 12/26 11Z 0.03 0025  45   6 -14 0.00
Fri 12/26 12Z 0.03 0022  40   6 -14 0.00
Fri 12/26 13Z 0.03 0019  35   7 -13 0.00
Fri 12/26 14Z 0.04 0017  29   7 -12 0.00
Fri 12/26 15Z 0.06 0114  25   7 -11 0.00
Fri 12/26 16Z 0.04 0111  25   8 -11 0.00
Fri 12/26 17Z 0.03 0108  23   8  -9 0.00
Fri 12/26 18Z 0.06 0207  22   7  -8 0.00
Fri 12/26 19Z 0.07 0406  21   8  -8 0.00
Fri 12/26 20Z 0.10 0706  20  14  -7 0.00
Fri 12/26 21Z 0.11 0907  20  46  -6 0.00
Fri 12/26 22Z 0.12 1208  19  64  -7 0.00
Fri 12/26 23Z 0.14 1312  19  72  -7 0.00
Sat 12/27 00Z 0.14 1415  21  74  -8 0.00
Sat 12/27 01Z 0.14 1517  26  80 -10 0.00
Sat 12/27 02Z 0.10 1618  53  88 -11 0.01
Sat 12/27 03Z 0.14 1518  68  90 -11 0.06
Sat 12/27 04Z 0.15 1517  76  90 -10 0.06
Sat 12/27 05Z 0.17 1416  85  90 -10 0.04
Sat 12/27 06Z 0.15 1415  88  89 -10 0.03
Sat 12/27 07Z 0.12 1513  88  87 -10 0.03
Sat 12/27 08Z 0.09 1510  89  87 -10 0.03
Sat 12/27 09Z 0.07 1507  89  86 -11 0.02
Sat 12/27 10Z 0.07 1304  89  83 -11 0.01
Sat 12/27 11Z 0.07 1003  88  81 -11 0.00
Sat 12/27 12Z 0.04 0302  84  77 -11 0.00
Sat 12/27 13Z 0.04 0005  80  73 -11 0.00
Sat 12/27 14Z 0.06 0107  76  69 -11 0.00
Sat 12/27 15Z 0.05 0108  71  69 -10 0.00
Sat 12/27 16Z 0.05 0108  66  68 -10 0.00
Sat 12/27 17Z 0.02 0008  61  69  -9 0.00
Sat 12/27 18Z 0.02 0009  55  69  -8 0.00
Sat 12/27 19Z 0.03 3510  50  68  -8 0.00
Sat 12/27 20Z 0.03 3513  39  61  -8 0.00
Sat 12/27 21Z 0.03 3515  30  55  -8 0.00
Sat 12/27 22Z 0.03 3516  20  48  -7 0.00
Sat 12/27 23Z 0.02 3516  11  38  -5 0.00
Sun 12/28 00Z 0.02 3516   8  28  -4 0.00
Sun 12/28 01Z 0.03 3516   7  33  -4 0.00
Sun 12/28 02Z 0.04 3516   7  31  -4 0.00
Sun 12/28 03Z 0.06 3416   9  28  -3 0.00
Sun 12/28 04Z 0.07 3416  12  20  -3 0.00
Sun 12/28 05Z 0.09 3417  15  13  -4 0.00
Sun 12/28 06Z 0.12 3317  23  11  -3 0.00
Sun 12/28 07Z 0.13 3318  28   8  -3 0.00
Sun 12/28 08Z 0.14 3319  32   5  -3 0.00
Sun 12/28 09Z 0.13 3319  34   9  -2 0.00
Sun 12/28 10Z 0.11 3319  35  12  -1 0.00
Sun 12/28 11Z 0.10 3418  36  13   0 0.00
Sun 12/28 12Z 0.10 3318  36  12   0 0.00
Sun 12/28 13Z 0.10 3317  35  17   0 0.00
Sun 12/28 14Z 0.11 3316  34  25   1 0.00
Sun 12/28 15Z 0.12 3316  34  36   1 0.00
Sun 12/28 16Z 0.13 3215  33  33   1 0.00
Sun 12/28 17Z 0.15 3215  34  41   2 0.00

Run total areal avg QPF for the greens is: 0.29 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