Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261026_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)
=== ===== === ==== ==== === === === ====
Mon 10/26 00Z 0.27 2611  28  19  10 0.00
Mon 10/26 01Z 0.33 2613  27  18  10 0.00
Mon 10/26 02Z 0.33 2714  25  17  10 0.00
Mon 10/26 03Z 0.34 2714  23  16  10 0.00
Mon 10/26 04Z 0.35 2714  21  14  10 0.00
Mon 10/26 05Z 0.37 2715  19  14  10 0.00
Mon 10/26 06Z 0.39 2716  17  14  10 0.00
Mon 10/26 07Z 0.41 2817  18  15  10 0.00
Mon 10/26 08Z 0.42 2817  18  17  10 0.00
Mon 10/26 09Z 0.42 2817  19  18  10 0.00
Mon 10/26 10Z 0.43 2818  25  27   9 0.00
Mon 10/26 11Z 0.43 2818  32  38   9 0.00
Mon 10/26 12Z 0.45 2919  36  50   9 0.00
Mon 10/26 13Z 0.46 2920  41  61   9 0.00
Mon 10/26 14Z 0.47 2821  49  69   9 0.00
Mon 10/26 15Z 0.49 2821  58  78   8 0.00
Mon 10/26 16Z 0.50 2921  68  83   8 0.00
Mon 10/26 17Z 0.48 2921  77  85   8 0.01
Mon 10/26 18Z 0.50 2921  88  88   7 0.02
Mon 10/26 19Z 0.53 2921  90  91   6 0.02
Mon 10/26 20Z 0.53 3021  89  92   5 0.02
Mon 10/26 21Z 0.51 3021  87  91   4 0.02
Mon 10/26 22Z 0.48 3122  80  85   3 0.01
Mon 10/26 23Z 0.50 3124  80  78   2 0.01
Tue 10/27 00Z 0.48 3224  81  77   1 0.01
Tue 10/27 01Z 0.36 3324  81  69   0 0.01
Tue 10/27 02Z 0.30 3323  85  57   0 0.01
Tue 10/27 03Z 0.22 3421  84  37  -1 0.00
Tue 10/27 04Z 0.17 3420  83  25  -2 0.00
Tue 10/27 05Z 0.13 3419  78  18  -2 0.00
Tue 10/27 06Z 0.11 3419  73  10  -3 0.00
Tue 10/27 07Z 0.10 3418  67   7  -3 0.00
Tue 10/27 08Z 0.09 3418  61   4  -2 0.00
Tue 10/27 09Z 0.09 3418  54   2  -2 0.00
Tue 10/27 10Z 0.09 3419  49   2  -1 0.00
Tue 10/27 11Z 0.09 3419  45   2  -1 0.00
Tue 10/27 12Z 0.09 3419  42   3  -1 0.00
Tue 10/27 13Z 0.08 3418  41   4  -1 0.00
Tue 10/27 14Z 0.08 3417  41   5  -1 0.00
Tue 10/27 15Z 0.08 3415  41   5  -1 0.00
Tue 10/27 16Z 0.08 3413  41   6  -1 0.00
Tue 10/27 17Z 0.10 3413  42   6  -1 0.00
Tue 10/27 18Z 0.09 3413  40   6  -1 0.00
Tue 10/27 19Z 0.09 3412  40   7  -1 0.00
Tue 10/27 20Z 0.09 3412  39   8  -1 0.00
Tue 10/27 21Z 0.09 3411  36  10  -1 0.00
Tue 10/27 22Z 0.09 3312  31  11  -1 0.00
Tue 10/27 23Z 0.09 3312  26  13   0 0.00
Wed 10/28 00Z 0.09 3312  23  15   0 0.00
Wed 10/28 01Z 0.08 3411  22  15   0 0.00
Wed 10/28 02Z 0.06 3410  20  16   0 0.00
Wed 10/28 03Z 0.05 3409  18  16   0 0.00
Wed 10/28 04Z 0.04 3407  17  16   1 0.00
Wed 10/28 05Z 0.05 3306  16  17   1 0.00
Wed 10/28 06Z 0.05 3305  16  16   1 0.00
Wed 10/28 07Z 0.05 3204  15  15   2 0.00
Wed 10/28 08Z 0.07 3004  14  14   2 0.00
Wed 10/28 09Z 0.09 2804  13  13   2 0.00
Wed 10/28 10Z 0.11 2805  13  13   2 0.00
Wed 10/28 11Z 0.12 2706  12  12   2 0.00

Run total areal avg QPF for the greens is: 0.14 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