NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260324_0000
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 03/24 00Z 0.16 3321  92  26 -10 0.00
Tue 03/24 01Z 0.24 3326  92  24 -10 0.00
Tue 03/24 02Z 0.42 3329  94  37 -11 0.00
Tue 03/24 03Z 0.44 3326  94  34 -11 0.00
Tue 03/24 04Z 0.35 3324  91  30 -11 0.01
Tue 03/24 05Z 0.27 3323  93  18 -10 0.01
Tue 03/24 06Z 0.16 3321  93  17 -11 0.00
Tue 03/24 07Z 0.12 3420  93  18 -11 0.00
Tue 03/24 08Z 0.09 3419  92  15 -11 0.00
Tue 03/24 09Z 0.08 3418  90   9 -11 0.00
Tue 03/24 10Z 0.11 3317  87   6 -11 0.00
Tue 03/24 11Z 0.14 3317  83   5 -11 0.00
Tue 03/24 12Z 0.18 3317  82   7 -11 0.00
Tue 03/24 13Z 0.20 3215  80  10 -11 0.00
Tue 03/24 14Z 0.25 3212  74  12 -11 0.00
Tue 03/24 15Z 0.40 3109  66  10 -11 0.00
Tue 03/24 16Z 0.63 2906  55   6 -10 0.00
Tue 03/24 17Z 0.81 2606  45   5  -9 0.00
Tue 03/24 18Z 1.67 2508  44   5  -9 0.00
Tue 03/24 19Z 1.25 2408  41   3  -8 0.00
Tue 03/24 20Z 1.41 2311  40   6  -8 0.00
Tue 03/24 21Z 1.17 2314  41   8  -7 0.00
Tue 03/24 22Z 0.90 2318  42  17  -7 0.00
Tue 03/24 23Z 0.93 2422  42  40  -6 0.00
Wed 03/25 00Z 1.23 2427  43  17  -6 0.00
Wed 03/25 01Z 1.70 2530  45  26  -7 0.00
Wed 03/25 02Z 3.46 2532  55  46  -8 0.00
Wed 03/25 03Z 3.23 2631  71  91  -8 0.00
Wed 03/25 04Z 1.82 2729  78  91  -9 0.00
Wed 03/25 05Z 1.08 2827  86  17  -9 0.01
Wed 03/25 06Z 1.15 2827  88  14  -9 0.00
Wed 03/25 07Z 0.83 2824  84   6  -9 0.00
Wed 03/25 08Z 0.60 2923  73  14  -8 0.00
Wed 03/25 09Z 0.49 2922  66  23  -7 0.00
Wed 03/25 10Z 0.55 2822  67  23  -8 0.00
Wed 03/25 11Z 0.45 2820  56  25  -7 0.00
Wed 03/25 12Z 0.40 2819  43  13  -5 0.00
Wed 03/25 13Z 0.36 2816  33  11  -4 0.00
Wed 03/25 14Z 0.34 2715  33   8  -4 0.00
Wed 03/25 15Z 0.40 2715  41   8  -5 0.00
Wed 03/25 16Z 0.41 2614  37   5  -4 0.00
Wed 03/25 17Z 0.45 2513  32   3  -4 0.00
Wed 03/25 18Z 0.48 2412  30  16  -4 0.00
Wed 03/25 19Z 0.57 2313  28  64  -4 0.00
Wed 03/25 20Z 1.06 2214  36  93  -4 0.00
Wed 03/25 21Z 2.00 2316  55  91  -4 0.00
Wed 03/25 22Z 1.84 2317  73  92  -5 0.00
Wed 03/25 23Z 0.74 2218  79  92  -4 0.00
Thu 03/26 00Z 0.75 2121  74  79  -3 0.00
Thu 03/26 01Z 0.84 2224  73  76  -3 0.00
Thu 03/26 02Z 0.78 2125  69  82  -2 0.00
Thu 03/26 03Z 0.94 2228  80  77  -2 0.00
Thu 03/26 04Z 0.89 2230  83  88  -2 0.00
Thu 03/26 05Z 0.75 2327  74  91  -1 0.00
Thu 03/26 06Z 0.77 2330  81  93  -1 0.00
Thu 03/26 07Z 0.78 2430  83  93  -1 0.00
Thu 03/26 08Z 0.69 2428  79  92   0 0.00
Thu 03/26 09Z 0.64 2426  73  94   0 0.00
Thu 03/26 10Z 0.60 2327  68  92   0 0.00
Thu 03/26 11Z 0.61 2426  72  93   1 0.00

Run total areal avg QPF for the Central_Greens is: 0.03 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