NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260215_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 02/15 18Z 0.24 0907  51  47  -8 0.00
Sun 02/15 19Z 0.22 1007  52  58  -8 0.00
Sun 02/15 20Z 0.14 1207  50  62  -7 0.00
Sun 02/15 21Z 0.10 1408  45  60  -6 0.00
Sun 02/15 22Z 0.07 1509  40  57  -6 0.00
Sun 02/15 23Z 0.08 1512  35  47  -6 0.00
Mon 02/16 00Z 0.08 1513  34  33  -5 0.00
Mon 02/16 01Z 0.09 1514  33  17  -5 0.00
Mon 02/16 04Z 0.03 1618  31   9  -6 0.00
Mon 02/16 05Z 0.06 1718  35  21  -6 0.00
Mon 02/16 06Z 0.07 1717  41  46  -7 0.00
Mon 02/16 07Z 0.06 1717  49  69  -7 0.00
Mon 02/16 08Z 0.04 1716  58  81  -6 0.00
Mon 02/16 09Z 0.04 1714  68  89  -6 0.00
Mon 02/16 10Z 0.04 1713  77  88  -6 0.00
Mon 02/16 11Z 0.03 1713  80  90  -6 0.00
Mon 02/16 12Z 0.04 1712  82  92  -5 0.00
Mon 02/16 13Z 0.05 1812  85  88  -5 0.00
Mon 02/16 14Z 0.06 1811  88  86  -5 0.00
Mon 02/16 15Z 0.07 1811  90  83  -5 0.00
Mon 02/16 16Z 0.07 1810  91  77  -5 0.00
Mon 02/16 17Z 0.06 1809  89  69  -4 0.00
Mon 02/16 18Z 0.08 1908  88  62  -4 0.00
Mon 02/16 19Z 0.07 1908  87  53  -4 0.00
Mon 02/16 20Z 0.13 1909  87  49  -5 0.00
Mon 02/16 21Z 0.14 2009  87  43  -5 0.00
Mon 02/16 22Z 0.08 1810  86  39  -4 0.00
Mon 02/16 23Z 0.17 1913  88  38  -5 0.00
Tue 02/17 00Z 0.20 2013  90  39  -5 0.00
Tue 02/17 01Z 0.24 2114  91  47  -5 0.00
Tue 02/17 02Z 0.24 2113  90  85  -4 0.00
Tue 02/17 03Z 0.27 2116  91  84  -4 0.00
Tue 02/17 04Z 0.24 2114  89  90  -3 0.00
Tue 02/17 05Z 0.27 2216  89  87  -3 0.00
Tue 02/17 06Z 0.28 2217  88  73  -3 0.00
Tue 02/17 07Z 0.31 2217  88  90  -2 0.00
Tue 02/17 08Z 0.27 2214  90  93  -2 0.00
Tue 02/17 09Z 0.27 2314  93  94  -3 0.00
Tue 02/17 10Z 0.30 2215  95  97  -3 0.00
Tue 02/17 11Z 0.31 2216  94  97  -3 0.00
Tue 02/17 12Z 0.30 2315  93  95  -3 0.01
Tue 02/17 13Z 0.30 2414  93  87  -3 0.01
Tue 02/17 14Z 0.30 2513  96  77  -3 0.01
Tue 02/17 15Z 0.30 2512  97  56  -3 0.00
Tue 02/17 16Z 0.28 2711  97  48  -3 0.01
Tue 02/17 17Z 0.28 2811  97  22  -3 0.01
Tue 02/17 18Z 0.32 2812  97  12  -3 0.01
Tue 02/17 19Z 0.31 2913  97  12  -3 0.00
Tue 02/17 20Z 0.34 2914  96  18  -3 0.00
Tue 02/17 21Z 0.42 2916  93  21  -3 0.00
Tue 02/17 22Z 0.44 2818  81  15  -3 0.00
Tue 02/17 23Z 0.40 2919  65  14  -2 0.00
Wed 02/18 00Z 0.39 2920  58  11  -2 0.01
Wed 02/18 01Z 0.40 2921  54  15  -2 0.01
Wed 02/18 02Z 0.39 3021  51  19  -3 0.00
Wed 02/18 03Z 0.42 2922  49  20  -3 0.00
Wed 02/18 04Z 0.43 2923  49  23  -3 0.00
Wed 02/18 05Z 0.41 3024  52  22  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 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