Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20240717_1200
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 07/17 12Z 0.46 2516  94  81  15 0.00
Wed 07/17 13Z 0.50 2518  94  93  15 0.00
Wed 07/17 14Z 0.58 2419  90  85  15 0.00
Wed 07/17 15Z 0.70 2417  90  86  15 0.00
Wed 07/17 16Z 0.76 2315  84  92  16 0.00
Wed 07/17 17Z 0.96 2214  80  88  16 0.00
Wed 07/17 18Z 0.60 2012  79  89  16 0.02
Wed 07/17 19Z 1.31 2917  90  87  15 0.58
Wed 07/17 20Z 0.57 2918  86  85  16 0.73
Wed 07/17 21Z 0.58 2916  83  67  16 0.03
Wed 07/17 22Z 0.58 2814  78  55  15 0.00
Wed 07/17 23Z 0.48 2612  79  58  15 0.00
Thu 07/18 00Z 0.42 2513  89  55  15 0.00
Thu 07/18 01Z 0.52 2614  93  61  15 0.01
Thu 07/18 02Z 0.64 2616  94  59  14 0.04
Thu 07/18 03Z 0.70 2715  89  58  13 0.03
Thu 07/18 04Z 0.62 2715  83  60  13 0.00
Thu 07/18 05Z 0.57 2715  77  58  14 0.00
Thu 07/18 06Z 0.71 2816  86  52  13 0.00
Thu 07/18 07Z 0.78 2916  84  54  12 0.00
Thu 07/18 08Z 0.70 2916  90  55  12 0.00
Thu 07/18 09Z 0.55 2915  90  57  12 0.00
Thu 07/18 10Z 0.49 2915  84  55  12 0.00
Thu 07/18 11Z 0.46 2915  81  66  12 0.00
Thu 07/18 12Z 0.50 2816  76  28  12 0.00
Thu 07/18 13Z 0.53 2816  77  37  11 0.00
Thu 07/18 14Z 0.61 2816  75  25  11 0.00
Thu 07/18 15Z 0.92 2815  76  18  10 0.00
Thu 07/18 16Z 1.33 2815  81  23  10 0.00
Thu 07/18 17Z 1.41 2716  89  22  10 0.00
Thu 07/18 18Z 1.38 2717  90  16  10 0.00
Thu 07/18 19Z 1.19 2817  89  19  10 0.00
Thu 07/18 20Z 1.39 2818  82  19  10 0.00
Thu 07/18 21Z 1.07 2918  84  21  10 0.00
Thu 07/18 22Z 0.94 2918  85  21  10 0.00
Thu 07/18 23Z 0.84 2919  89  21   9 0.01
Fri 07/19 00Z 0.76 2920  91  18   9 0.01
Fri 07/19 01Z 0.74 3021  93  17   9 0.01
Fri 07/19 02Z 0.65 3020  93  19   8 0.02
Fri 07/19 03Z 0.61 3019  93  20   8 0.02
Fri 07/19 04Z 0.57 3118  94  23   8 0.01
Fri 07/19 05Z 0.52 3117  94  26   8 0.01
Fri 07/19 06Z 0.42 3114  92  32   8 0.01
Fri 07/19 07Z 0.31 3112  89  28   9 0.01
Fri 07/19 08Z 0.28 3213  88  31   9 0.00
Fri 07/19 09Z 0.27 3213  87  37   9 0.00
Fri 07/19 10Z 0.23 3312  82  34   9 0.00
Fri 07/19 11Z 0.21 3311  75  32   9 0.00
Fri 07/19 12Z 0.19 3209  74  32   9 0.00
Fri 07/19 13Z 0.17 3208  73  30  10 0.00
Fri 07/19 14Z 0.19 3108  75  29   9 0.00
Fri 07/19 15Z 0.20 3108  76  25  10 0.00
Fri 07/19 16Z 0.20 3207  75  23  10 0.00
Fri 07/19 17Z 0.23 3107  75  21  10 0.00
Fri 07/19 18Z 0.27 3007  73  17  10 0.00
Fri 07/19 19Z 0.38 2907  71  14  10 0.00
Fri 07/19 20Z 0.47 2907  72  11  10 0.00
Fri 07/19 21Z 0.51 2807  78  11  10 0.00
Fri 07/19 22Z 0.48 2708  85  15  10 0.00
Fri 07/19 23Z 0.51 2609  87  19  10 0.00

Run total areal avg QPF for the Northern_Greens is: 1.55 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