NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260808_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 08/08 18Z 0.88 2307  94  63  16 0.00
Sat 08/08 19Z 0.64 2311  93  55  16 0.00
Sat 08/08 20Z 0.55 2314  89  58  16 0.00
Sat 08/08 21Z 0.61 2413  88  52  17 0.00
Sat 08/08 22Z 0.68 2414  91  65  16 0.04
Sat 08/08 23Z 0.61 2516  90  67  16 0.12
Sun 08/09 00Z 0.53 2616  83  69  16 0.14
Sun 08/09 01Z 0.52 2717  84  66  16 0.05
Sun 08/09 02Z 0.39 2813  87  53  16 0.00
Sun 08/09 03Z 0.42 2713  90  43  16 0.00
Sun 08/09 04Z 0.49 2715  91  35  15 0.00
Sun 08/09 05Z 0.52 2616  88  35  16 0.00
Sun 08/09 06Z 0.62 2619  92  37  16 0.00
Sun 08/09 07Z 0.63 2520  90  58  16 0.00
Sun 08/09 08Z 0.74 2523  90  53  15 0.01
Sun 08/09 09Z 0.71 2623  93  54  15 0.01
Sun 08/09 10Z 0.61 2722  89  59  15 0.01
Sun 08/09 11Z 0.55 2820  88  48  15 0.01
Sun 08/09 12Z 0.55 2820  91  47  15 0.01
Sun 08/09 13Z 0.53 2818  93  30  15 0.01
Sun 08/09 14Z 0.46 2917  88  21  15 0.00
Sun 08/09 15Z 0.42 2816  78  20  15 0.00
Sun 08/09 16Z 0.50 2815  79  14  15 0.01
Sun 08/09 17Z 0.80 2715  87  16  14 0.01
Sun 08/09 18Z 0.62 2816  87  20  14 0.01
Sun 08/09 19Z 0.59 2816  87  30  15 0.01
Sun 08/09 20Z 0.65 2916  85  32  15 0.01
Sun 08/09 21Z 0.51 2915  80  27  15 0.01
Sun 08/09 22Z 0.43 2914  74  30  15 0.00
Sun 08/09 23Z 0.44 2916  69  27  16 0.00
Mon 08/10 00Z 0.44 2916  66  31  16 0.00
Mon 08/10 01Z 0.43 2916  66  28  16 0.00
Mon 08/10 02Z 0.37 2916  71  32  16 0.00
Mon 08/10 03Z 0.31 2915  67  33  17 0.00
Mon 08/10 04Z 0.31 2915  64  33  17 0.00
Mon 08/10 05Z 0.28 2914  56  36  17 0.00
Mon 08/10 06Z 0.26 3014  48  37  17 0.00
Mon 08/10 07Z 0.23 3012  46  35  16 0.00
Mon 08/10 08Z 0.23 3011  48  35  15 0.00
Mon 08/10 09Z 0.19 3110  52  34  15 0.00
Mon 08/10 10Z 0.08 3207  54  34  15 0.00
Mon 08/10 11Z 0.03 3302  55  34  15 0.00
Mon 08/10 12Z 0.05 2102  56  31  15 0.00
Mon 08/10 13Z 0.12 2006  55  35  15 0.00
Mon 08/10 14Z 0.19 2108  54  54  15 0.00
Mon 08/10 15Z 0.23 2109  54  61  15 0.00
Mon 08/10 16Z 0.33 2210  54  87  15 0.00
Mon 08/10 17Z 0.37 2211  49  84  15 0.00
Mon 08/10 18Z 0.51 2312  52  64  15 0.00
Mon 08/10 19Z 0.65 2312  60  57  15 0.00
Mon 08/10 20Z 0.41 2310  62  69  16 0.00
Mon 08/10 21Z 0.48 2311  71  65  15 0.00
Mon 08/10 22Z 0.49 2312  78  77  15 0.00
Mon 08/10 23Z 0.41 2113  84  87  15 0.01
Tue 08/11 00Z 0.52 2117  91  92  15 0.04
Tue 08/11 01Z 0.71 2221  93  92  14 0.08
Tue 08/11 02Z 0.80 2422  94  75  15 0.11
Tue 08/11 03Z 0.75 2621  96  69  14 0.01
Tue 08/11 04Z 0.78 2622  96  73  14 0.01
Tue 08/11 05Z 0.68 2620  95  37  14 0.01

Run total areal avg QPF for the Central_Greens is: 0.74 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