NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260412_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)
=== ===== === ==== ==== === === === ====
Sun 04/12 00Z 0.81 3118  74   8  -5 0.00
Sun 04/12 01Z 0.79 3121  76   9  -5 0.00
Sun 04/12 02Z 0.78 3223  78  12  -6 0.00
Sun 04/12 03Z 0.58 3223  73  13  -6 0.00
Sun 04/12 04Z 0.43 3223  67  12  -5 0.00
Sun 04/12 05Z 0.31 3322  63  11  -5 0.00
Sun 04/12 06Z 0.23 3321  60  11  -5 0.00
Sun 04/12 07Z 0.18 3320  58  11  -5 0.00
Sun 04/12 08Z 0.15 3318  56  13  -5 0.00
Sun 04/12 09Z 0.11 3315  54  17  -4 0.00
Sun 04/12 10Z 0.06 3414  50  22  -4 0.00
Sun 04/12 11Z 0.04 3411  48  23  -3 0.00
Sun 04/12 12Z 0.05 3308  46  20  -2 0.00
Sun 04/12 13Z 0.06 3204  47  23  -2 0.00
Sun 04/12 14Z 0.11 2703  48  27  -2 0.00
Sun 04/12 15Z 0.14 2304  47  24  -2 0.00
Sun 04/12 16Z 0.27 2106  45  36  -2 0.00
Sun 04/12 17Z 0.51 2007  43  71  -1 0.00
Sun 04/12 18Z 0.85 2009  42  95  -1 0.00
Sun 04/12 19Z 0.51 2011  39  92   0 0.00
Sun 04/12 20Z 0.29 1913  36  96   0 0.00
Sun 04/12 21Z 1.41 2016  50  96  -1 0.00
Sun 04/12 22Z 0.22 2015  95  99  -1 0.04
Sun 04/12 23Z 0.24 1919  97  99   0 0.04
Mon 04/13 00Z 0.33 2025  97  99   0 0.08
Mon 04/13 01Z 0.36 2025  97  99   0 0.05
Mon 04/13 02Z 0.40 2026  97  99   1 0.07
Mon 04/13 03Z 0.42 2127  97  99   1 0.08
Mon 04/13 04Z 0.43 2228  98  99   3 0.09
Mon 04/13 05Z 0.43 2228  98  99   5 0.09
Mon 04/13 06Z 0.45 2230  96  98   7 0.12
Mon 04/13 07Z 0.45 2331  89  95   9 0.04
Mon 04/13 08Z 0.48 2332  90  97   9 0.03
Mon 04/13 09Z 0.56 2336  90  96   9 0.04
Mon 04/13 10Z 0.64 2438  85  57  10 0.03
Mon 04/13 11Z 0.68 2438  84  62  10 0.00
Mon 04/13 12Z 0.69 2438  83  43  10 0.00
Mon 04/13 13Z 0.77 2540  89  61   9 0.00
Mon 04/13 14Z 0.85 2539  93  54   8 0.00
Mon 04/13 15Z 0.84 2537  84  64   8 0.00
Mon 04/13 16Z 0.92 2439  88  95   8 0.01
Mon 04/13 17Z 1.02 2441  95  97   8 0.02
Mon 04/13 18Z 1.13 2343  95  96   8 0.04
Mon 04/13 19Z 1.22 2343  97  96   8 0.07
Mon 04/13 20Z 1.20 2442  98  95   8 0.09
Mon 04/13 21Z 1.14 2540  98  93   8 0.07
Mon 04/13 22Z 1.06 2638  98  84   9 0.04
Mon 04/13 23Z 1.03 2637  98  56   9 0.04
Tue 04/14 00Z 1.00 2636  97  49   9 0.05
Tue 04/14 01Z 1.02 2735  97  69   9 0.04
Tue 04/14 02Z 1.03 2734  98  56   9 0.03
Tue 04/14 03Z 1.06 2734  98  49   8 0.03
Tue 04/14 04Z 1.00 2832  98  33   8 0.03
Tue 04/14 05Z 0.84 2929  98  23   7 0.02
Tue 04/14 06Z 0.71 3027  98  14   7 0.02
Tue 04/14 07Z 0.62 3125  99  14   6 0.02
Tue 04/14 08Z 0.48 3122  97  14   6 0.02
Tue 04/14 09Z 0.34 3120  91  13   7 0.01
Tue 04/14 10Z 0.25 3117  83   8   8 0.01
Tue 04/14 11Z 0.21 3014  75   9   9 0.01

Run total areal avg QPF for the Central_Greens is: 1.47 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