Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260625_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)
=== ===== === ==== ==== === === === ====
Thu 06/25 00Z 0.67 3015  78  57  10 0.00
Thu 06/25 01Z 0.99 2918  77  49  10 0.00
Thu 06/25 02Z 1.05 2920  78  41  10 0.00
Thu 06/25 03Z 0.99 2920  77  46  10 0.00
Thu 06/25 04Z 0.72 2920  79  52  10 0.00
Thu 06/25 05Z 0.61 2919  76  60  10 0.00
Thu 06/25 06Z 0.54 3018  73  62  10 0.00
Thu 06/25 07Z 0.54 3017  69  58  10 0.00
Thu 06/25 08Z 0.52 2915  65  39  10 0.00
Thu 06/25 09Z 0.46 2913  64  29  10 0.00
Thu 06/25 10Z 0.45 3012  62  30  10 0.00
Thu 06/25 11Z 0.39 3011  62  39  10 0.00
Thu 06/25 12Z 0.31 3008  63  47  10 0.00
Thu 06/25 13Z 0.27 3006  62  46  10 0.00
Thu 06/25 14Z 0.34 2804  63  46  10 0.00
Thu 06/25 15Z 0.87 2504  64  49  10 0.00
Thu 06/25 16Z 1.61 2405  64  46  10 0.00
Thu 06/25 17Z 3.00 2305  64  44  11 0.00
Thu 06/25 18Z 3.86 2306  65  47  11 0.00
Thu 06/25 19Z 4.58 2207  65  52  11 0.00
Thu 06/25 20Z 4.01 2208  66  53  11 0.00
Thu 06/25 21Z 2.77 2108  65  53  11 0.00
Thu 06/25 22Z 2.03 2108  63  57  11 0.00
Thu 06/25 23Z 0.82 2109  63  57  11 0.00
Fri 06/26 00Z 0.51 2010  61  70  11 0.00
Fri 06/26 01Z 0.55 2012  63  86  11 0.00
Fri 06/26 02Z 0.54 2014  68  94  11 0.00
Fri 06/26 03Z 0.39 1914  68  92  11 0.00
Fri 06/26 04Z 0.38 1914  75  88  11 0.00
Fri 06/26 05Z 0.43 1917  79  82  11 0.01
Fri 06/26 06Z 0.45 1920  84  87  10 0.01
Fri 06/26 07Z 0.41 1920  89  93  10 0.03
Fri 06/26 08Z 0.28 1919  91  93  11 0.10
Fri 06/26 09Z 0.21 1919  93  94  11 0.01
Fri 06/26 10Z 0.27 1923  95  95  11 0.09
Fri 06/26 11Z 0.35 2023  93  94  10 0.15
Fri 06/26 12Z 0.30 1920  92  90  10 0.01
Fri 06/26 13Z 0.32 2017  99  84  10 0.02
Fri 06/26 14Z 0.36 2214 100  72  10 0.04
Fri 06/26 15Z 0.33 2310  98  65  10 0.01
Fri 06/26 16Z 0.31 2408  97  41  10 0.00
Fri 06/26 17Z 0.37 2508  97  42  10 0.00
Fri 06/26 18Z 0.44 2608  95  54  10 0.00
Fri 06/26 19Z 0.45 2606  93  49  11 0.00
Fri 06/26 20Z 0.54 2606  92  48  11 0.00
Fri 06/26 21Z 0.42 2504  92  64  11 0.01
Fri 06/26 22Z 0.29 2505  92  88  12 0.10
Fri 06/26 23Z 0.29 2706  91  60  12 0.09
Sat 06/27 00Z 0.33 2808  93  65  12 0.03
Sat 06/27 01Z 0.28 2908  90  65  12 0.01
Sat 06/27 02Z 0.26 2908  89  69  11 0.00
Sat 06/27 03Z 0.24 2907  92  53  11 0.00
Sat 06/27 04Z 0.26 2808  94  43  11 0.00
Sat 06/27 05Z 0.28 2808  96  40  11 0.01
Sat 06/27 06Z 0.21 2706  94  37  11 0.01
Sat 06/27 07Z 0.19 2606  92  38  10 0.00
Sat 06/27 08Z 0.11 2703  92  37  10 0.00
Sat 06/27 09Z 0.10 2803  93  37  10 0.00
Sat 06/27 10Z 0.04 3001  91  35  10 0.00
Sat 06/27 11Z 0.03 0001  91  36  10 0.00

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