NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260915_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 09/15 00Z 0.57 3221  85  22   4 0.00
Tue 09/15 01Z 0.52 3323  84  23   4 0.00
Tue 09/15 02Z 0.15 3422  81  18   4 0.00
Tue 09/15 03Z 0.02 3520  79  14   5 0.00
Tue 09/15 04Z 0.07 3518  76  10   6 0.00
Tue 09/15 05Z 0.05 3516  75   8   6 0.00
Tue 09/15 06Z 0.13 0013  72   7   6 0.00
Tue 09/15 07Z 0.09 0109  68   6   7 0.00
Tue 09/15 08Z 0.08 0107  65   7   7 0.00
Tue 09/15 09Z 0.04 0005  67   8   6 0.00
Tue 09/15 10Z 0.03 0001  65  10   6 0.00
Tue 09/15 11Z 0.02 1100  63  12   7 0.00
Tue 09/15 12Z 0.03 1603  62  13   7 0.00
Tue 09/15 13Z 0.03 1803  59  15   7 0.00
Tue 09/15 14Z 0.05 1904  61  16   7 0.00
Tue 09/15 15Z 0.06 1905  62  16   8 0.00
Tue 09/15 16Z 0.10 2006  65  16   8 0.00
Tue 09/15 17Z 0.09 1907  65  15   9 0.00
Tue 09/15 18Z 0.15 2009  65  16   9 0.00
Tue 09/15 19Z 0.17 2009  63  15  10 0.00
Tue 09/15 20Z 0.20 2011  61  15  10 0.00
Tue 09/15 21Z 0.20 2012  57  13  11 0.00
Tue 09/15 22Z 0.22 2014  50  45  12 0.00
Tue 09/15 23Z 0.28 2116  48  83  12 0.00
Wed 09/16 00Z 0.22 2016  40  91  14 0.00
Wed 09/16 01Z 0.21 2019  36  90  15 0.00
Wed 09/16 02Z 0.26 2120  37  86  15 0.00
Wed 09/16 03Z 0.33 2222  38  88  15 0.00
Wed 09/16 04Z 0.37 2223  43  91  15 0.00
Wed 09/16 05Z 0.42 2323  47  94  15 0.00
Wed 09/16 06Z 0.46 2423  51  96  14 0.00
Wed 09/16 07Z 0.48 2423  50  95  14 0.00
Wed 09/16 08Z 0.46 2522  52  91  14 0.00
Wed 09/16 09Z 0.46 2522  57  79  14 0.00
Wed 09/16 10Z 0.48 2622  69  75  14 0.00
Wed 09/16 11Z 0.46 2721  82  68  14 0.00
Wed 09/16 12Z 0.43 2719  90  68  14 0.00
Wed 09/16 13Z 0.41 2818  92  76  14 0.00
Wed 09/16 14Z 0.42 2717  92  72  14 0.00
Wed 09/16 15Z 0.41 2716  91  75  14 0.00
Wed 09/16 16Z 0.42 2716  92  80  14 0.00
Wed 09/16 17Z 0.40 2615  94  82  15 0.00
Wed 09/16 18Z 0.37 2614  96  86  15 0.00
Wed 09/16 19Z 0.35 2713  97  84  15 0.01
Wed 09/16 20Z 0.32 2812  97  57  14 0.01
Wed 09/16 21Z 0.28 2811  96  58  14 0.00
Wed 09/16 22Z 0.26 2811  95  49  14 0.00
Wed 09/16 23Z 0.25 2911  94  38  14 0.00
Thu 09/17 00Z 0.18 2909  91  19  14 0.00
Thu 09/17 01Z 0.15 3008  89  20  14 0.00
Thu 09/17 02Z 0.14 3007  87  16  14 0.00
Thu 09/17 03Z 0.12 3007  82  18  14 0.00
Thu 09/17 04Z 0.11 3006  79  15  14 0.00
Thu 09/17 05Z 0.07 2903  77  27  14 0.00
Thu 09/17 06Z 0.09 2703  78  41  14 0.00
Thu 09/17 07Z 0.10 2404  79  41  14 0.00
Thu 09/17 08Z 0.13 2306  80  47  14 0.00
Thu 09/17 09Z 0.14 2306  81  54  14 0.00
Thu 09/17 10Z 0.16 2307  87  73  14 0.00
Thu 09/17 11Z 0.16 2307  91  80  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.02 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