NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20240921_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 09/21 00Z 0.38 1108  87  84  11 0.00
Sat 09/21 03Z 0.24 1210  88  73  10 0.01
Sat 09/21 06Z 0.15 0905  83  54  10 0.00
Sat 09/21 09Z 0.18 0807  82  41  10 0.00
Sat 09/21 12Z 0.16 0507  76  40  10 0.00
Sat 09/21 15Z 0.22 0708  71  30  10 0.00
Sat 09/21 18Z 0.18 0807  62  21  10 0.00
Sat 09/21 21Z 0.14 0905  58  13  10 0.00
Sun 09/22 00Z 0.16 1006  65  38   9 0.00
Sun 09/22 03Z 0.16 1107  74  31   9 0.00
Sun 09/22 06Z 0.18 1108  83  47   8 0.00
Sun 09/22 09Z 0.21 1008  89  67   7 0.00
Sun 09/22 12Z 0.22 0907  92  69   6 0.00
Sun 09/22 15Z 0.35 0912  84  55   7 0.00
Sun 09/22 18Z 0.44 1008  89  49   5 0.00
Sun 09/22 21Z 0.74 1009  89  32   5 0.00
Mon 09/23 00Z 0.64 1212  86  16   5 0.00
Mon 09/23 03Z 0.45 1314  88   8   4 0.00
Mon 09/23 06Z 0.41 1315  86  13   4 0.00
Mon 09/23 09Z 0.43 1217  84  19   5 0.00
Mon 09/23 12Z 0.36 1318  83  28   5 0.00
Mon 09/23 15Z 0.30 1415  83  43   5 0.00
Mon 09/23 18Z 1.11 1412  85  55   4 0.00
Mon 09/23 21Z 0.34 1415  84  42   5 0.00
Tue 09/24 00Z 0.19 1411  86  72   6 0.00
Tue 09/24 03Z 0.17 1513  77  79   7 0.00
Tue 09/24 06Z 0.10 1613  82  84   7 0.00
Tue 09/24 09Z 0.07 1611  88  86   7 0.00
Tue 09/24 12Z 0.11 1510  92  85   7 0.00

Run total areal avg QPF for the greens is: 0.01 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