BTV4 EXPERIMENTAL Froude Number for the Green Mountains

Subject: BTV4 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_BTV4_20190822_1800
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 08/22 18Z 1.81 2714  92  33  13 0.00
Thu 08/22 19Z 3.05 2716  90  40  13 0.01
Thu 08/22 20Z 5.80 2716  81  35  13 0.01
Thu 08/22 21Z 8.73 2716  78  38  13 0.00
Thu 08/22 22Z 3.24 2817  76  38  13 0.00
Thu 08/22 23Z 1.53 2817  73  38  12 0.00
Fri 08/23 00Z 1.32 2917  71  36  12 0.00
Fri 08/23 01Z 1.03 2918  70  36  11 0.00
Fri 08/23 02Z 0.83 3017  73  36  11 0.00
Fri 08/23 03Z 0.62 3015  79  35  10 0.00
Fri 08/23 04Z 0.50 3012  80  35  10 0.00
Fri 08/23 05Z 0.38 3110  83  37   9 0.00
Fri 08/23 06Z 0.34 3110  84  39   9 0.00
Fri 08/23 07Z 0.37 3011  86  43   9 0.00
Fri 08/23 08Z 0.38 3011  88  45   8 0.00
Fri 08/23 09Z 0.43 3012  88  47   8 0.00
Fri 08/23 10Z 0.50 2914  88  47   8 0.00
Fri 08/23 11Z 0.54 3016  89  45   8 0.00
Fri 08/23 12Z 0.56 3017  90  40   7 0.00
Fri 08/23 13Z 0.59 3118  91  32   7 0.00
Fri 08/23 14Z 0.64 3117  90  28   7 0.00
Fri 08/23 15Z 0.77 3116  86  27   7 0.00
Fri 08/23 16Z 1.51 3115  82  26   7 0.00
Fri 08/23 17Z 2.78 3114  80  25   7 0.00
Fri 08/23 18Z 5.13 3113  79  25   7 0.00
Fri 08/23 19Z 5.67 3113  78  26   8 0.00
Fri 08/23 20Z 5.65 3114  77  26   8 0.00
Fri 08/23 21Z 4.60 3114  76  25   8 0.00
Fri 08/23 22Z 2.29 3115  76  25   8 0.00
Fri 08/23 23Z 1.29 3216  76  24   8 0.00
Sat 08/24 00Z 1.04 3218  77  23   7 0.00
Sat 08/24 01Z 1.27 3319  78  22   7 0.00
Sat 08/24 02Z 1.17 3319  77  21   7 0.00
Sat 08/24 03Z 0.58 3319  77  20   6 0.00
Sat 08/24 04Z 0.27 3417  76  20   6 0.00
Sat 08/24 05Z 0.21 3415  75  21   6 0.00
Sat 08/24 06Z 0.19 3314  73  21   7 0.00
Sat 08/24 07Z 0.17 3312  72  22   7 0.00
Sat 08/24 08Z 0.14 3312  71  23   7 0.00
Sat 08/24 09Z 0.11 3413  71  23   7 0.00
Sat 08/24 10Z 0.08 3413  71  24   7 0.00
Sat 08/24 11Z 0.04 3513  72  25   7 0.00
Sat 08/24 12Z 0.02 3514  74  27   7 0.00
Sat 08/24 13Z 0.04 0012  77  29   8 0.00
Sat 08/24 14Z 0.08 0111  80  31   8 0.00
Sat 08/24 15Z 0.11 0210  82  31   8 0.00
Sat 08/24 16Z 0.15 0209  84  30   8 0.00
Sat 08/24 17Z 0.20 0208  85  29   8 0.00
Sat 08/24 18Z 0.28 0308  85  28   8 0.00
Sat 08/24 19Z 0.38 0307  85  27   8 0.00
Sat 08/24 20Z 0.42 0307  86  26   8 0.00
Sat 08/24 21Z 0.33 0407  87  26   8 0.00
Sat 08/24 22Z 0.34 0408  87  26   8 0.00
Sat 08/24 23Z 0.33 0509  86  26   8 0.00
Sun 08/25 00Z 0.38 0510  87  26   8 0.00
Sun 08/25 01Z 0.38 0609  84  26   9 0.00
Sun 08/25 02Z 0.35 0809  81  26   9 0.00
Sun 08/25 03Z 0.36 1009  83  26   9 0.00
Sun 08/25 04Z 0.38 1109  86  26   8 0.00
Sun 08/25 05Z 0.32 1209  89  27   8 0.00
Sun 08/25 06Z 0.27 1310  92  28   8 0.00
Sun 08/25 07Z 0.23 1310  93  29   8 0.00
Sun 08/25 08Z 0.21 1308  92  29   8 0.00
Sun 08/25 09Z 0.20 1107  88  28   8 0.00
Sun 08/25 10Z 0.19 1006  85  27   8 0.00
Sun 08/25 11Z 0.18 0905  84  27   7 0.00
Sun 08/25 12Z 0.18 0906  83  27   7 0.00
Sun 08/25 13Z 0.18 0906  82  27   7 0.00
Sun 08/25 14Z 0.22 0906  82  27   7 0.00
Sun 08/25 15Z 0.28 1007  82  26   7 0.00
Sun 08/25 16Z 0.38 1008  82  26   7 0.00
Sun 08/25 17Z 0.64 1008  83  26   7 0.00
Sun 08/25 18Z 1.58 1108  82  25   7 0.00
Sun 08/25 19Z 2.39 1109  80  24   7 0.00
Sun 08/25 20Z 2.91 1209  79  23   8 0.00
Sun 08/25 21Z 2.49 1209  78  22   8 0.00
Sun 08/25 22Z 1.43 1210  77  21   8 0.00
Sun 08/25 23Z 0.81 1210  74  20   8 0.00
Mon 08/26 00Z 0.50 1210  69  19   8 0.00
Mon 08/26 01Z 0.35 1209  64  19   8 0.00
Mon 08/26 02Z 0.23 1208  59  18   8 0.00
Mon 08/26 03Z 0.22 1107  52  17   8 0.00
Mon 08/26 04Z 0.23 1108  48  18   8 0.00
Mon 08/26 05Z 0.22 1108  45  18   8 0.00

Run total areal avg QPF for the greens is: 0.02 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