NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260521_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)
=== ===== === ==== ==== === === === ====
Thu 05/21 06Z 0.24 3318  76   9   4 0.00
Thu 05/21 07Z 0.24 3321  73   8   3 0.00
Thu 05/21 08Z 0.21 3421  72   8   2 0.00
Thu 05/21 09Z 0.18 3420  70   7   2 0.00
Thu 05/21 10Z 0.16 3419  65   7   1 0.00
Thu 05/21 11Z 0.16 3318  62   5   1 0.00
Thu 05/21 12Z 0.17 3315  60   3   0 0.00
Thu 05/21 13Z 0.18 3314  57   2   0 0.00
Thu 05/21 14Z 0.18 3313  54   3   0 0.00
Thu 05/21 15Z 0.20 3312  51   4   0 0.00
Thu 05/21 16Z 0.27 3312  48   4   0 0.00
Thu 05/21 17Z 0.33 3312  46   4   0 0.00
Thu 05/21 18Z 0.45 3312  44   5   0 0.00
Thu 05/21 19Z 0.47 3313  42   4   0 0.00
Thu 05/21 20Z 0.48 3313  42   4   0 0.00
Thu 05/21 21Z 0.41 3313  44   4   0 0.00
Thu 05/21 22Z 0.30 3313  46   3   0 0.00
Thu 05/21 23Z 0.25 3313  47   3   0 0.00
Fri 05/22 00Z 0.18 3414  46   2   0 0.00
Fri 05/22 01Z 0.15 3415  47   2   0 0.00
Fri 05/22 02Z 0.11 3515  47   2   0 0.00
Fri 05/22 03Z 0.08 3515  47   2   0 0.00
Fri 05/22 04Z 0.09 3514  50   2   0 0.00
Fri 05/22 05Z 0.08 0013  52   2   0 0.00
Fri 05/22 06Z 0.08 0012  52   2   0 0.00
Fri 05/22 07Z 0.14 0111  51   2   0 0.00
Fri 05/22 08Z 0.11 0111  50   2   0 0.00
Fri 05/22 09Z 0.14 0212  45   2   0 0.00
Fri 05/22 10Z 0.13 0211  40   2   0 0.00
Fri 05/22 11Z 0.16 0212  37   2   0 0.00
Fri 05/22 12Z 0.17 0211  35   2   0 0.00
Fri 05/22 13Z 0.17 0309  34   2   0 0.00
Fri 05/22 14Z 0.18 0307  35   2   0 0.00
Fri 05/22 15Z 0.32 0306  37   3   0 0.00
Fri 05/22 16Z 0.47 0204  39   4   0 0.00
Fri 05/22 17Z 0.80 0303  40   5   1 0.00
Fri 05/22 18Z 0.76 0202  42   6   2 0.00
Fri 05/22 19Z 0.74 0202  44   7   2 0.00
Fri 05/22 20Z 0.49 0102  46   9   3 0.00
Fri 05/22 21Z 0.45 0002  47  11   3 0.00
Fri 05/22 22Z 0.22 0003  47  11   3 0.00
Fri 05/22 23Z 0.09 0103  46  13   4 0.00
Sat 05/23 00Z 0.11 0303  45  14   4 0.00
Sat 05/23 01Z 0.13 0403  43  15   4 0.00
Sat 05/23 02Z 0.17 0603  41  18   4 0.00
Sat 05/23 03Z 0.18 0603  40  17   4 0.00
Sat 05/23 04Z 0.21 0704  40  14   4 0.00
Sat 05/23 05Z 0.21 0704  41  13   4 0.00
Sat 05/23 06Z 0.26 0705  42  11   4 0.00
Sat 05/23 07Z 0.31 0806  43  10   4 0.00
Sat 05/23 08Z 0.32 0806  42   9   4 0.00
Sat 05/23 09Z 0.34 0907  41   8   4 0.00
Sat 05/23 10Z 0.35 1008  41   7   4 0.00
Sat 05/23 11Z 0.36 1109  41   6   4 0.00
Sat 05/23 12Z 0.38 1110  41   6   4 0.00
Sat 05/23 13Z 0.40 1211  44   6   4 0.00
Sat 05/23 14Z 0.47 1211  46   7   4 0.00
Sat 05/23 15Z 0.70 1310  49   7   4 0.00
Sat 05/23 16Z 1.66 1308  53   7   4 0.00
Sat 05/23 17Z 1.78 1407  54   8   4 0.00

Run total areal avg QPF for the 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