NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260826_1200
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)
=== ===== === ==== ==== === === === ====
Wed 08/26 12Z 0.04 3305  89  39  10 0.00
Wed 08/26 13Z 0.04 3304  89  38  10 0.00
Wed 08/26 14Z 0.03 3101  90  37  10 0.00
Wed 08/26 15Z 0.05 2301  90  37  10 0.00
Wed 08/26 16Z 0.06 2101  91  36  10 0.00
Wed 08/26 17Z 0.13 2302  91  34  10 0.00
Wed 08/26 18Z 0.23 2303  90  32  10 0.00
Wed 08/26 19Z 0.17 2103  87  29  11 0.00
Wed 08/26 20Z 0.14 1903  86  22  11 0.00
Wed 08/26 21Z 0.18 2004  87  18  11 0.00
Wed 08/26 22Z 0.16 1905  87  14  11 0.00
Wed 08/26 23Z 0.20 2006  88  14  11 0.00
Thu 08/27 00Z 0.22 2008  89  12  11 0.00
Thu 08/27 01Z 0.19 1908  88   9  11 0.00
Thu 08/27 02Z 0.18 2009  85  10  11 0.00
Thu 08/27 03Z 0.18 2009  83  11  11 0.00
Thu 08/27 04Z 0.22 2010  81  12  11 0.00
Thu 08/27 05Z 0.25 2111  78  15  12 0.00
Thu 08/27 06Z 0.27 2112  76  19  12 0.00
Thu 08/27 07Z 0.36 2114  79  18  11 0.00
Thu 08/27 08Z 0.42 2115  87  18  11 0.00
Thu 08/27 09Z 0.54 2117  89  16  11 0.00
Thu 08/27 10Z 0.56 2118  90  15  11 0.00
Thu 08/27 11Z 0.64 2120  89  26  11 0.00
Thu 08/27 12Z 0.66 2122  91  64  11 0.00
Thu 08/27 13Z 0.71 2123  90  66  11 0.00
Thu 08/27 14Z 0.68 2023  87  63  12 0.00
Thu 08/27 15Z 0.88 2022  88  53  12 0.00
Thu 08/27 16Z 0.74 2020  92  51  12 0.00
Thu 08/27 17Z 0.76 2022  94  74  13 0.01
Thu 08/27 18Z 0.48 2021  96  58  13 0.01
Thu 08/27 19Z 0.57 2022  96  65  13 0.02
Thu 08/27 20Z 0.54 1924  95  68  13 0.01
Thu 08/27 21Z 0.47 2021  87  49  14 0.02
Thu 08/27 22Z 0.44 1923  93  45  14 0.00
Thu 08/27 23Z 0.49 2026  93  58  14 0.00
Fri 08/28 00Z 0.50 2025  91  68  15 0.00
Fri 08/28 01Z 0.74 2131  96  75  14 0.01
Fri 08/28 02Z 0.69 2228  90  60  14 0.05
Fri 08/28 03Z 0.76 2228  95  63  14 0.08
Fri 08/28 04Z 0.76 2326  91  66  13 0.06
Fri 08/28 05Z 0.69 2323  94  61  13 0.01
Fri 08/28 06Z 0.64 2322  95  60  13 0.02
Fri 08/28 07Z 0.61 2419  95  62  13 0.01
Fri 08/28 08Z 0.52 2516  93  59  13 0.01
Fri 08/28 09Z 0.49 2515  93  56  12 0.01
Fri 08/28 10Z 0.43 2514  92  46  12 0.00
Fri 08/28 11Z 0.36 2512  92  49  12 0.00
Fri 08/28 12Z 0.35 2512  91  45  12 0.00
Fri 08/28 13Z 0.32 2510  90  46  12 0.00
Fri 08/28 14Z 0.29 2509  90  32  12 0.00
Fri 08/28 15Z 0.28 2507  92  30  12 0.00
Fri 08/28 16Z 0.30 2507  93  21  12 0.00
Fri 08/28 17Z 0.32 2607  92  21  12 0.00
Fri 08/28 18Z 0.37 2607  92  16  12 0.00
Fri 08/28 19Z 0.37 2708  94  11  12 0.00
Fri 08/28 20Z 0.34 2808  96   9  12 0.01
Fri 08/28 21Z 0.30 2809  95  12  12 0.01
Fri 08/28 22Z 0.25 2909  94  11  12 0.01
Fri 08/28 23Z 0.23 3009  94  14  11 0.01

Run total areal avg QPF for the Central_Greens is: 0.37 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