Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261024_1800
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)
=== ===== === ==== ==== === === === ====
Sat 10/24 18Z 0.10 3106  36   1   5 0.00
Sat 10/24 19Z 0.07 3206  39   1   5 0.00
Sat 10/24 20Z 0.07 3205  39   1   5 0.00
Sat 10/24 21Z 0.08 3105  38   2   6 0.00
Sat 10/24 22Z 0.11 3106  38   2   6 0.00
Sat 10/24 23Z 0.13 3007  36   3   6 0.00
Sun 10/25 00Z 0.15 3008  35   3   6 0.00
Sun 10/25 01Z 0.12 3107  36   3   6 0.00
Sun 10/25 02Z 0.10 3106  35   3   6 0.00
Sun 10/25 03Z 0.09 3106  33   3   7 0.00
Sun 10/25 04Z 0.09 3005  31   3   7 0.00
Sun 10/25 05Z 0.12 2805  27   3   7 0.00
Sun 10/25 06Z 0.13 2806  21   3   8 0.00
Sun 10/25 07Z 0.13 2806  18   2   8 0.00
Sun 10/25 08Z 0.13 2806  17   2   8 0.00
Sun 10/25 09Z 0.13 2706  16   2   8 0.00
Sun 10/25 10Z 0.14 2706  16   3   8 0.00
Sun 10/25 11Z 0.15 2707  17   5   8 0.00
Sun 10/25 12Z 0.18 2708  18   7   8 0.00
Sun 10/25 13Z 0.19 2709  17   8   8 0.00
Sun 10/25 14Z 0.18 2708  14  10   9 0.00
Sun 10/25 15Z 0.16 2607  12  11   9 0.00
Sun 10/25 16Z 0.18 2608  13  10   9 0.00
Sun 10/25 17Z 0.19 2608  14   9   9 0.00
Sun 10/25 18Z 0.20 2609  14  12   9 0.00
Sun 10/25 19Z 0.22 2610  14  13   9 0.00
Sun 10/25 20Z 0.22 2510  13  12   9 0.00
Sun 10/25 21Z 0.24 2611  13  13  10 0.00
Sun 10/25 22Z 0.27 2612  15  14  10 0.00
Sun 10/25 23Z 0.28 2613  16  16  10 0.00
Mon 10/26 00Z 0.29 2613  17  16  11 0.00
Mon 10/26 01Z 0.30 2614  17  15  11 0.00
Mon 10/26 02Z 0.31 2615  15  14  11 0.00
Mon 10/26 03Z 0.32 2616  11  14  11 0.00
Mon 10/26 04Z 0.32 2616  11  14  11 0.00
Mon 10/26 05Z 0.35 2618  15  14  11 0.00
Mon 10/26 06Z 0.36 2718  15  13  11 0.00
Mon 10/26 07Z 0.33 2717  15  11  11 0.00
Mon 10/26 08Z 0.33 2817  19   9  11 0.00
Mon 10/26 09Z 0.34 2818  22  10  10 0.00
Mon 10/26 10Z 0.36 2919  28  13  10 0.00
Mon 10/26 11Z 0.36 2919  29  14  10 0.00
Mon 10/26 12Z 0.38 2919  37  33  10 0.00
Mon 10/26 13Z 0.41 2920  47  39   9 0.00
Mon 10/26 14Z 0.45 2922  63  56   9 0.00
Mon 10/26 15Z 0.46 2922  84  68   8 0.00
Mon 10/26 16Z 0.45 2923  94  84   8 0.01
Mon 10/26 17Z 0.40 3022  96  90   7 0.01
Mon 10/26 18Z 0.39 3021  91  90   6 0.01
Mon 10/26 19Z 0.43 3021  87  89   5 0.00
Mon 10/26 20Z 0.42 3020  84  90   4 0.01
Mon 10/26 21Z 0.40 3120  84  63   3 0.01
Mon 10/26 22Z 0.39 3123  86  33   3 0.01
Mon 10/26 23Z 0.35 3224  89  25   1 0.01
Tue 10/27 00Z 0.26 3224  84  23   0 0.01
Tue 10/27 01Z 0.18 3323  83  19   0 0.00
Tue 10/27 02Z 0.11 3423  80  16  -1 0.00
Tue 10/27 03Z 0.06 3423  78  14  -2 0.00
Tue 10/27 04Z 0.04 3423  74  16  -2 0.00
Tue 10/27 05Z 0.05 3424  71  16  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 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