Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260505_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)
=== ===== === ==== ==== === === === ====
Tue 05/05 18Z 10.91 2124  57  72  12 0.00
Tue 05/05 19Z 13.08 2127  56  78  12 0.00
Tue 05/05 20Z 12.65 2127  58  94  12 0.00
Tue 05/05 21Z 4.79 2129  70  95  12 0.01
Tue 05/05 22Z 2.68 2225  73  97  11 0.06
Tue 05/05 23Z 0.90 2533  88  88   9 0.34
Wed 05/06 00Z 0.74 2427  85  71   9 0.01
Wed 05/06 01Z 0.65 2423  89  90   9 0.01
Wed 05/06 02Z 0.63 2421  96  95   8 0.09
Wed 05/06 03Z 0.63 2518  97  99   7 0.08
Wed 05/06 04Z 0.56 2716  95  98   6 0.07
Wed 05/06 05Z 0.46 2714  96  93   5 0.08
Wed 05/06 06Z 0.46 2714  96  91   5 0.05
Wed 05/06 07Z 0.38 2614  93  67   5 0.01
Wed 05/06 08Z 0.34 2513  94  76   5 0.01
Wed 05/06 09Z 0.27 2411  95  67   6 0.01
Wed 05/06 10Z 0.20 2111  93  77   6 0.01
Wed 05/06 11Z 0.15 1913  96  82   7 0.00
Wed 05/06 12Z 0.14 1914  98  80   7 0.01
Wed 05/06 13Z 0.12 1816  98  83   7 0.04
Wed 05/06 14Z 0.24 1920  98  93   7 0.07
Wed 05/06 15Z 0.26 1921  99  96   7 0.07
Wed 05/06 16Z 0.25 1921  98  98   8 0.10
Wed 05/06 17Z 0.29 1925  99  97   8 0.09
Wed 05/06 18Z 0.43 2026  99  98   8 0.19
Wed 05/06 19Z 0.50 2124  99  98   8 0.21
Wed 05/06 20Z 0.45 2123  99  98   8 0.11
Wed 05/06 21Z 0.33 2018 100  99   8 0.07
Wed 05/06 22Z 0.21 2310  99  98   7 0.08
Wed 05/06 23Z 0.15 2808  98  99   6 0.10
Thu 05/07 00Z 0.12 3008  96  97   5 0.05
Thu 05/07 01Z 0.09 3209  94  98   4 0.02
Thu 05/07 02Z 0.12 3212  92  97   3 0.02
Thu 05/07 03Z 0.11 3211  90  95   3 0.01
Thu 05/07 04Z 0.17 3113  90  96   2 0.00
Thu 05/07 05Z 0.23 3014  92  87   1 0.01
Thu 05/07 06Z 0.27 3014  93  78   1 0.00
Thu 05/07 07Z 0.30 3016  93  42   0 0.00
Thu 05/07 08Z 0.31 3016  91  30   0 0.01
Thu 05/07 09Z 0.42 3017  91  35   0 0.01
Thu 05/07 10Z 0.48 2918  88  12  -1 0.00
Thu 05/07 11Z 0.55 2820  80  13  -1 0.00
Thu 05/07 12Z 0.52 2818  67  11  -2 0.00
Thu 05/07 13Z 0.53 2816  59  13  -2 0.00
Thu 05/07 14Z 0.57 2915  62  13  -2 0.00
Thu 05/07 15Z 2.37 2814  72  15  -2 0.00
Thu 05/07 16Z 7.92 2813  75  15  -2 0.00
Thu 05/07 17Z 9.16 2813  71  17  -1 0.00
Thu 05/07 18Z 8.84 2813  67  19   0 0.00
Thu 05/07 19Z 9.14 2814  65  19   0 0.00
Thu 05/07 20Z 8.63 2813  64  18   0 0.00
Thu 05/07 21Z 7.62 2812  61  18   0 0.00
Thu 05/07 22Z 7.04 2912  59  19   0 0.00
Thu 05/07 23Z 4.32 2912  59  22   0 0.00
Fri 05/08 00Z 1.33 2914  62  21   0 0.00
Fri 05/08 01Z 1.07 3015  69  19  -1 0.00
Fri 05/08 02Z 1.05 3016  76  16  -2 0.00
Fri 05/08 03Z 0.96 2916  77  17  -2 0.00
Fri 05/08 04Z 0.80 2916  77  18  -2 0.00
Fri 05/08 05Z 0.70 2917  76  20  -2 0.00

Run total areal avg QPF for the Central_Greens is: 2.11 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