NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260423_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 04/23 18Z 4.67 3218  61   9   0 0.00
Thu 04/23 19Z 3.61 3217  59   8   0 0.00
Thu 04/23 20Z 2.67 3317  57   6   0 0.00
Thu 04/23 21Z 2.35 3318  55   8   0 0.00
Thu 04/23 22Z 1.45 3318  55  13   0 0.00
Thu 04/23 23Z 0.68 3320  54  10   0 0.00
Fri 04/24 00Z 0.46 3322  52   6   0 0.00
Fri 04/24 01Z 0.38 3323  50   4   0 0.00
Fri 04/24 02Z 0.21 3422  50   6  -1 0.00
Fri 04/24 03Z 0.19 3418  54   5  -2 0.00
Fri 04/24 04Z 0.25 3515  59   5  -2 0.00
Fri 04/24 05Z 0.24 0012  64   7  -3 0.00
Fri 04/24 06Z 0.16 0010  68   8  -4 0.00
Fri 04/24 07Z 0.04 3409  69   9  -4 0.00
Fri 04/24 08Z 0.11 3310  70   8  -5 0.00
Fri 04/24 09Z 0.15 3312  72   8  -5 0.00
Fri 04/24 10Z 0.14 3315  73   6  -6 0.00
Fri 04/24 11Z 0.07 3417  70   5  -5 0.00
Fri 04/24 12Z 0.09 3416  70  12  -5 0.00
Fri 04/24 13Z 0.11 3414  70  32  -5 0.00
Fri 04/24 14Z 0.23 3413  70  44  -5 0.00
Fri 04/24 15Z 0.65 3411  69  49  -5 0.00
Fri 04/24 16Z 0.51 3410  66  37  -4 0.00
Fri 04/24 17Z 1.12 3310  65  21  -4 0.00
Fri 04/24 18Z 0.51 3411  65  13  -3 0.00
Fri 04/24 19Z 0.53 3410  66   9  -3 0.00
Fri 04/24 20Z 0.48 3410  67   7  -3 0.00
Fri 04/24 21Z 0.28 3410  69   8  -3 0.00
Fri 04/24 22Z 0.95 0010  71   8  -3 0.00
Fri 04/24 23Z 1.02 0111  74  11  -3 0.00
Sat 04/25 00Z 0.60 0112  75  14  -4 0.00
Sat 04/25 01Z 0.80 0213  78  15  -4 0.00
Sat 04/25 02Z 0.91 0314  80  15  -4 0.00
Sat 04/25 03Z 0.80 0417  80  13  -4 0.00
Sat 04/25 04Z 0.62 0515  76  12  -4 0.00
Sat 04/25 05Z 0.45 0513  73   9  -4 0.00
Sat 04/25 06Z 0.33 0710  72   6  -4 0.00
Sat 04/25 07Z 0.25 0907  72   4  -4 0.00
Sat 04/25 08Z 0.22 1107  74   3  -4 0.00
Sat 04/25 09Z 0.17 1207  76   3  -4 0.00
Sat 04/25 10Z 0.13 1308  78   3  -4 0.00
Sat 04/25 11Z 0.14 1308  78   3  -4 0.00
Sat 04/25 12Z 0.12 1307  77   4  -4 0.00
Sat 04/25 13Z 0.14 1307  75   3  -4 0.00
Sat 04/25 14Z 0.13 1306  74   3  -4 0.00
Sat 04/25 15Z 0.44 1405  73   3  -4 0.00
Sat 04/25 16Z 0.84 1404  70   4  -3 0.00
Sat 04/25 17Z 1.46 1203  67   4  -2 0.00
Sat 04/25 18Z 1.11 1202  65   4  -1 0.00
Sat 04/25 19Z 1.47 0902  63   4  -1 0.00
Sat 04/25 20Z 1.49 0903  62   4   0 0.00
Sat 04/25 21Z 1.44 0903  61   4   0 0.00
Sat 04/25 22Z 0.77 0903  60   4   0 0.00
Sat 04/25 23Z 0.43 0904  60   4   0 0.00
Sun 04/26 00Z 0.36 1005  61   4   0 0.00
Sun 04/26 01Z 0.31 1106  63   5   0 0.00
Sun 04/26 02Z 0.23 1205  61   5   0 0.00
Sun 04/26 03Z 0.22 1004  60   5   0 0.00
Sun 04/26 04Z 0.24 0905  59   6   0 0.00
Sun 04/26 05Z 0.27 0806  57   6   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.00 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