Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261018_0600
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)
=== ===== === ==== ==== === === === ====
Sun 10/18 06Z 0.29 3013  73  55  -3 0.00
Sun 10/18 07Z 0.41 2915  72  59  -3 0.00
Sun 10/18 08Z 0.48 2915  71  61  -3 0.00
Sun 10/18 09Z 0.48 2917  70  68  -2 0.00
Sun 10/18 10Z 0.41 3018  82  73  -2 0.00
Sun 10/18 11Z 0.39 3018  85  75  -1 0.00
Sun 10/18 12Z 0.37 3016  80  72  -1 0.00
Sun 10/18 13Z 0.37 3016  79  61   0 0.00
Sun 10/18 14Z 0.37 2914  82  49   0 0.00
Sun 10/18 15Z 0.37 2913  81  42   0 0.00
Sun 10/18 16Z 0.37 2811  77  41   0 0.00
Sun 10/18 17Z 0.39 2611  67  39   1 0.00
Sun 10/18 18Z 0.37 2611  54  38   2 0.00
Sun 10/18 19Z 0.34 2611  43  36   3 0.00
Sun 10/18 20Z 0.31 2512  40  31   4 0.00
Sun 10/18 21Z 0.30 2613  37  24   5 0.00
Sun 10/18 22Z 0.29 2613  36  15   6 0.00
Sun 10/18 23Z 0.27 2713  35  10   7 0.00
Mon 10/19 00Z 0.25 2712  33  10   8 0.00
Mon 10/19 01Z 0.22 2711  28  11   8 0.00
Mon 10/19 02Z 0.21 2710  21  12   8 0.00
Mon 10/19 03Z 0.21 2710  17  13   8 0.00
Mon 10/19 04Z 0.21 2610  18  14   9 0.00
Mon 10/19 05Z 0.20 2609  19  15   9 0.00
Mon 10/19 06Z 0.20 2609  20  16   9 0.00
Mon 10/19 07Z 0.21 2509  20  17   9 0.00
Mon 10/19 08Z 0.22 2610  20  17   9 0.00
Mon 10/19 09Z 0.22 2610  20  17  10 0.00
Mon 10/19 10Z 0.22 2610  19  17  10 0.00
Mon 10/19 11Z 0.23 2711  19  18  10 0.00
Mon 10/19 12Z 0.22 2711  17  17  10 0.00
Mon 10/19 13Z 0.20 2810  16  18  10 0.00
Mon 10/19 14Z 0.19 2709  15  18  10 0.00
Mon 10/19 15Z 0.19 2708  15  20  10 0.00
Mon 10/19 16Z 0.17 2607  15  20  10 0.00
Mon 10/19 17Z 0.17 2607  15  20  10 0.00
Mon 10/19 18Z 0.17 2707  14  20  11 0.00
Mon 10/19 19Z 0.17 2807  13  20  11 0.00
Mon 10/19 20Z 0.16 2908  13  20  11 0.00
Mon 10/19 21Z 0.17 3009  13  21  11 0.00
Mon 10/19 22Z 0.17 3111  14  21  11 0.00
Mon 10/19 23Z 0.14 3212  15  21  11 0.00
Tue 10/20 00Z 0.10 3312  19  21  11 0.00
Tue 10/20 01Z 0.07 3312  24  21  10 0.00
Tue 10/20 02Z 0.04 3412  29  18  10 0.00
Tue 10/20 03Z 0.03 3512  34  14  10 0.00
Tue 10/20 04Z 0.04 3513  37  10  10 0.00
Tue 10/20 05Z 0.04 3515  39   9  10 0.00
Tue 10/20 06Z 0.07 0017  43  10   9 0.00
Tue 10/20 07Z 0.11 0018  40  12   9 0.00
Tue 10/20 08Z 0.16 0119  40  18   9 0.00
Tue 10/20 09Z 0.18 0120  32  23   9 0.00
Tue 10/20 10Z 0.20 0122  21  19   9 0.00
Tue 10/20 11Z 0.24 0223  15  14   9 0.00
Tue 10/20 12Z 0.25 0223  15   7   9 0.00
Tue 10/20 13Z 0.25 0222  17   2   9 0.00
Tue 10/20 14Z 0.23 0222  19   2   8 0.00
Tue 10/20 15Z 0.23 0220  23   2   8 0.00
Tue 10/20 16Z 0.21 0218  30   2   7 0.00
Tue 10/20 17Z 0.20 0216  36   3   7 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