NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260425_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)
=== ===== === ==== ==== === === === ====
Sat 04/25 00Z 0.28 0210  69  15  -2 0.00
Sat 04/25 01Z 0.40 0413  71  17  -2 0.00
Sat 04/25 02Z 0.43 0415  70  18  -2 0.00
Sat 04/25 03Z 0.49 0418  68  19  -3 0.00
Sat 04/25 04Z 0.51 0518  67  18  -3 0.00
Sat 04/25 05Z 0.44 0714  67  17  -3 0.00
Sat 04/25 06Z 0.39 1012  68  16  -3 0.00
Sat 04/25 07Z 0.29 1211  69  17  -3 0.00
Sat 04/25 08Z 0.21 1310  71  18  -3 0.00
Sat 04/25 09Z 0.16 1410  73  18  -3 0.00
Sat 04/25 10Z 0.13 1409  75  19  -2 0.00
Sat 04/25 11Z 0.11 1508  76  19  -3 0.00
Sat 04/25 12Z 0.08 1506  76  18  -3 0.00
Sat 04/25 13Z 0.09 1404  74  17  -3 0.00
Sat 04/25 14Z 0.15 1204  71  17  -2 0.00
Sat 04/25 15Z 0.50 1203  69  16  -2 0.00
Sat 04/25 16Z 1.00 1203  67  16  -2 0.00
Sat 04/25 18Z 1.00 1202  65  16   0 0.00
Sat 04/25 19Z 1.08 1102  64  17   0 0.00
Sat 04/25 20Z 1.07 1102  65  17   0 0.00
Sat 04/25 21Z 0.80 1103  65  17   0 0.00
Sat 04/25 22Z 0.47 1103  65  18   0 0.00
Sat 04/25 23Z 0.30 1003  65  18   0 0.00
Sun 04/26 00Z 0.24 1003  65  18   0 0.00
Sun 04/26 01Z 0.24 0804  64  20   0 0.00
Sun 04/26 02Z 0.31 0705  63  21   0 0.00
Sun 04/26 03Z 0.30 0706  62  21   0 0.00
Sun 04/26 04Z 0.35 0707  60  21   0 0.00
Sun 04/26 05Z 0.35 0707  60  21   0 0.00
Sun 04/26 06Z 0.34 0807  59  21   0 0.00
Sun 04/26 07Z 0.33 0807  59  22   0 0.00
Sun 04/26 08Z 0.34 0807  58  22   0 0.00
Sun 04/26 09Z 0.33 0907  58  18   0 0.00
Sun 04/26 10Z 0.34 0906  57  16   0 0.00
Sun 04/26 11Z 0.33 0906  57  14   0 0.00
Sun 04/26 12Z 0.36 1006  58  13   0 0.00
Sun 04/26 13Z 0.45 0905  60  12   0 0.00
Sun 04/26 14Z 1.27 0803  62  10   0 0.00
Sun 04/26 15Z 1.26 0402  64   9   0 0.00
Sun 04/26 16Z 1.12 0203  64  10   0 0.00
Sun 04/26 17Z 1.13 0303  63  12   1 0.00
Sun 04/26 18Z 0.99 0203  61  12   2 0.00
Sun 04/26 19Z 0.98 0203  60   9   2 0.00
Sun 04/26 20Z 0.84 0203  60   9   3 0.00
Sun 04/26 21Z 1.15 0405  60  11   3 0.00
Sun 04/26 22Z 1.02 0405  61  18   3 0.00
Sun 04/26 23Z 0.56 0506  61  28   3 0.00
Mon 04/27 00Z 0.53 0508  62  34   3 0.00
Mon 04/27 01Z 0.59 0609  63  38   3 0.00
Mon 04/27 02Z 0.56 0709  64  47   3 0.00
Mon 04/27 03Z 0.45 0807  66  52   3 0.00
Mon 04/27 04Z 0.41 0807  67  52   3 0.00
Mon 04/27 05Z 0.43 0908  68  52   3 0.00
Mon 04/27 06Z 0.42 0908  69  54   3 0.00
Mon 04/27 07Z 0.41 0909  71  55   3 0.00
Mon 04/27 08Z 0.40 0910  66  54   3 0.00
Mon 04/27 09Z 0.38 0910  65  56   3 0.00
Mon 04/27 10Z 0.36 1010  60  56   3 0.00
Mon 04/27 11Z 0.34 1010  54  53   3 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