NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260814_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)
=== ===== === ==== ==== === === === ====
Fri 08/14 18Z 1.32 3310  82  63  10 0.00
Fri 08/14 19Z 1.13 3311  75  70  10 0.00
Fri 08/14 20Z 0.66 3310  74  71  10 0.00
Fri 08/14 21Z 0.88 3212  76  66  10 0.00
Fri 08/14 22Z 0.32 3212  76  57  10 0.00
Fri 08/14 23Z 0.23 3313  76  54  10 0.00
Sat 08/15 00Z 0.30 3315  78  58  10 0.00
Sat 08/15 01Z 0.16 3417  78  51  10 0.00
Sat 08/15 02Z 0.13 3417  81  39   9 0.00
Sat 08/15 03Z 0.10 3416  82  32   9 0.00
Sat 08/15 04Z 0.08 3415  84  26   8 0.00
Sat 08/15 05Z 0.03 3413  83  22   8 0.00
Sat 08/15 06Z 0.03 3411  82  17   8 0.00
Sat 08/15 07Z 0.09 3310  80  15   8 0.00
Sat 08/15 08Z 0.13 3310  77  11   9 0.00
Sat 08/15 09Z 0.21 3212  76   9   8 0.00
Sat 08/15 10Z 0.26 3214  78   9   8 0.00
Sat 08/15 11Z 0.27 3215  79   9   8 0.00
Sat 08/15 12Z 0.22 3215  81   9   8 0.00
Sat 08/15 13Z 0.17 3314  82  10   8 0.00
Sat 08/15 14Z 0.12 3312  79  11   8 0.00
Sat 08/15 15Z 0.15 3309  79  11   8 0.00
Sat 08/15 16Z 0.18 3209  80  12   8 0.00
Sat 08/15 17Z 0.24 3209  80  10   8 0.00
Sat 08/15 18Z 0.34 3210  77   8   8 0.00
Sat 08/15 19Z 0.56 3211  73   6   8 0.00
Sat 08/15 20Z 0.78 3211  73   6   8 0.00
Sat 08/15 21Z 0.34 3210  72   5   9 0.00
Sat 08/15 22Z 0.16 3210  67   6   9 0.00
Sat 08/15 23Z 0.07 3310  62   9   9 0.00
Sun 08/16 00Z 0.07 3309  60   8   9 0.00
Sun 08/16 01Z 0.05 3409  56   7   9 0.00
Sun 08/16 02Z 0.07 3309  56   7   9 0.00
Sun 08/16 03Z 0.05 3409  58   8   9 0.00
Sun 08/16 04Z 0.03 3407  56   9  10 0.00
Sun 08/16 05Z 0.02 3405  53   8  10 0.00
Sun 08/16 06Z 0.04 3304  52   7  10 0.00
Sun 08/16 07Z 0.02 3302  51   6  11 0.00
Sun 08/16 08Z 0.02 2800  51   9  11 0.00
Sun 08/16 09Z 0.05 2003  55  10  10 0.00
Sun 08/16 10Z 0.11 2205  60  12  10 0.00
Sun 08/16 11Z 0.10 2006  64  12  10 0.00
Sun 08/16 12Z 0.20 2109  74  11   9 0.00
Sun 08/16 13Z 0.25 2111  81  11   9 0.00
Sun 08/16 14Z 0.28 2212  82   9   9 0.00
Sun 08/16 15Z 0.31 2211  80   5  10 0.00
Sun 08/16 16Z 0.34 2210  83   3  10 0.00
Sun 08/16 17Z 0.33 2109  84   4  10 0.00
Sun 08/16 18Z 0.32 2009  86   6  10 0.00
Sun 08/16 19Z 0.24 1910  89   6  11 0.00
Sun 08/16 20Z 0.27 1911  91  21  11 0.00
Sun 08/16 21Z 0.26 1912  92  24  11 0.00
Sun 08/16 22Z 0.24 1914  96  31  11 0.00
Sun 08/16 23Z 0.34 2017  93  46  11 0.00
Mon 08/17 00Z 0.43 2019  93  54  12 0.00
Mon 08/17 01Z 0.40 2021  95  87  12 0.01
Mon 08/17 02Z 0.43 2025  97  76  12 0.01
Mon 08/17 03Z 0.52 2126  98  79  12 0.03
Mon 08/17 04Z 0.59 2126  97  91  12 0.03
Mon 08/17 05Z 0.56 2128  97  93  13 0.03

Run total areal avg QPF for the Central_Greens is: 0.11 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