NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260419_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)
=== ===== === ==== ==== === === === ====
Sun 04/19 18Z 0.34 3117  98  92  -4 0.00
Sun 04/19 19Z 0.59 3018  94  89  -5 0.00
Sun 04/19 20Z 0.67 3018  95  87  -6 0.01
Sun 04/19 21Z 0.72 3017  94  75  -6 0.02
Sun 04/19 22Z 0.79 2916  92  22  -6 0.00
Sun 04/19 23Z 0.91 2817  93  26  -5 0.00
Mon 04/20 00Z 1.18 2722  93  40  -5 0.00
Mon 04/20 01Z 1.56 2825  92  50  -6 0.01
Mon 04/20 02Z 1.52 2926  90  49  -6 0.01
Mon 04/20 03Z 1.32 2925  82  24  -7 0.00
Mon 04/20 04Z 1.27 2824  73  33  -7 0.00
Mon 04/20 05Z 1.09 2824  68  47  -7 0.00
Mon 04/20 06Z 0.94 2822  71  40  -7 0.00
Mon 04/20 07Z 0.92 2822  75  34  -7 0.00
Mon 04/20 08Z 0.87 2821  80  43  -7 0.00
Mon 04/20 09Z 0.80 2819  82  56  -8 0.00
Mon 04/20 10Z 0.74 2818  82  60  -8 0.00
Mon 04/20 11Z 0.70 2816  88  59  -9 0.00
Mon 04/20 12Z 0.61 2813  92  67  -9 0.00
Mon 04/20 13Z 0.54 2911  93  50  -9 0.01
Mon 04/20 14Z 1.02 3010  93  40  -9 0.01
Mon 04/20 15Z 1.32 3110  93  47  -9 0.00
Mon 04/20 16Z 0.90 3210  90  49  -9 0.00
Mon 04/20 17Z 1.58 3209  82  53  -9 0.00
Mon 04/20 18Z 2.61 3109  73  55  -9 0.00
Mon 04/20 19Z 3.77 3110  66  57  -8 0.00
Mon 04/20 20Z 4.24 3110  63  51  -8 0.00
Mon 04/20 21Z 3.75 3110  63  53  -8 0.00
Mon 04/20 22Z 2.51 3110  62  43  -8 0.00
Mon 04/20 23Z 1.23 3210  61  33  -8 0.00
Tue 04/21 00Z 0.42 3211  60  26  -9 0.00
Tue 04/21 01Z 0.31 3312  58  15  -9 0.00
Tue 04/21 02Z 0.34 3313  54  10  -9 0.00
Tue 04/21 03Z 0.40 3313  52   7  -9 0.00
Tue 04/21 04Z 0.35 3313  50   7 -10 0.00
Tue 04/21 05Z 0.38 3312  50   9 -10 0.00
Tue 04/21 06Z 0.39 3212  50  13 -10 0.00
Tue 04/21 07Z 0.41 3211  49  13 -10 0.00
Tue 04/21 08Z 0.38 3210  48  11 -10 0.00
Tue 04/21 09Z 0.37 3109  47  12 -10 0.00
Tue 04/21 10Z 0.32 3007  47  13 -10 0.00
Tue 04/21 11Z 0.30 3006  46  13 -10 0.00
Tue 04/21 12Z 0.47 2804  47  11 -10 0.00
Tue 04/21 13Z 1.70 2504  46  11 -10 0.00
Tue 04/21 14Z 2.42 2304  44  11  -9 0.00
Tue 04/21 15Z 3.19 2205  43  11  -9 0.00
Tue 04/21 16Z 3.47 2206  41  11  -8 0.00
Tue 04/21 17Z 4.31 2207  40  16  -7 0.00
Tue 04/21 18Z 4.74 2307  39  43  -6 0.00
Tue 04/21 19Z 4.11 2307  38  69  -6 0.00
Tue 04/21 20Z 3.75 2307  38  87  -5 0.00
Tue 04/21 21Z 2.62 2306  38  84  -5 0.00
Tue 04/21 22Z 1.53 2206  37  74  -5 0.00
Tue 04/21 23Z 0.44 2207  37  63  -4 0.00
Wed 04/22 00Z 0.40 2109  38  58  -4 0.00
Wed 04/22 01Z 0.40 2110  41  68  -4 0.00
Wed 04/22 02Z 0.46 2112  43  81  -4 0.00
Wed 04/22 03Z 0.58 2114  46  89  -4 0.00
Wed 04/22 04Z 0.63 2116  48  90  -4 0.00
Wed 04/22 05Z 0.66 2116  50  86  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.07 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