NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260816_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 08/16 18Z 0.71 2007  86   9  12 0.00
Sun 08/16 19Z 0.85 2008  86  12  12 0.00
Sun 08/16 20Z 0.52 2010  87  23  13 0.01
Sun 08/16 21Z 0.43 2011  84  20  13 0.01
Sun 08/16 22Z 0.27 1911  84  31  13 0.00
Sun 08/16 23Z 0.24 1914  92  93  13 0.00
Mon 08/17 00Z 0.34 1917  97  92  13 0.03
Mon 08/17 01Z 0.57 2123  97  95  13 0.04
Mon 08/17 02Z 0.63 2126  97  87  13 0.02
Mon 08/17 03Z 0.57 2128  98  78  13 0.01
Mon 08/17 04Z 0.59 2128  98  80  13 0.02
Mon 08/17 05Z 0.60 2130  98  81  13 0.02
Mon 08/17 06Z 0.55 2129  98  84  13 0.02
Mon 08/17 07Z 0.57 2230  97  87  14 0.02
Mon 08/17 08Z 0.57 2229  98  89  14 0.02
Mon 08/17 09Z 0.54 2227  98  91  14 0.03
Mon 08/17 10Z 0.49 2224  98  94  14 0.02
Mon 08/17 11Z 0.48 2222  98  94  14 0.03
Mon 08/17 12Z 0.46 2221  98  91  14 0.02
Mon 08/17 13Z 0.41 2218  99  90  14 0.03
Mon 08/17 14Z 0.35 2314  99  88  14 0.02
Mon 08/17 15Z 0.26 2211  97  88  15 0.01
Mon 08/17 16Z 0.24 2209  97  91  15 0.00
Mon 08/17 17Z 0.26 2308  98  91  14 0.01
Mon 08/17 18Z 0.21 2406  98  88  15 0.01
Mon 08/17 19Z 0.16 2504  97  85  15 0.00
Mon 08/17 20Z 0.12 2803  97  76  15 0.00
Mon 08/17 21Z 0.10 3104  97  72  15 0.00
Mon 08/17 22Z 0.06 3304  97  49  15 0.00
Mon 08/17 23Z 0.05 3305  96  34  15 0.00
Tue 08/18 00Z 0.03 3406  95  36  15 0.00
Tue 08/18 01Z 0.05 3508  97  37  14 0.01
Tue 08/18 02Z 0.07 0010  96  23  14 0.01
Tue 08/18 03Z 0.07 0009  95  18  14 0.01
Tue 08/18 04Z 0.08 0009  94  35  14 0.00
Tue 08/18 05Z 0.07 0009  93  28  14 0.00
Tue 08/18 06Z 0.04 3509  92  14  14 0.01
Tue 08/18 07Z 0.03 3509  90   7  14 0.00
Tue 08/18 08Z 0.04 3508  88   6  14 0.00
Tue 08/18 09Z 0.04 3508  87   3  14 0.00
Tue 08/18 10Z 0.04 3507  85   2  13 0.00
Tue 08/18 11Z 0.03 3506  83   2  13 0.00
Tue 08/18 12Z 0.02 3506  82   2  13 0.00
Tue 08/18 13Z 0.03 0005  81   1  13 0.00
Tue 08/18 14Z 0.02 3504  83   1  13 0.00
Tue 08/18 15Z 0.03 3303  83   2  12 0.00
Tue 08/18 16Z 0.07 3103  84   2  12 0.00
Tue 08/18 17Z 0.06 3203  83   2  12 0.00
Tue 08/18 18Z 0.06 3103  82   2  12 0.00
Tue 08/18 19Z 0.12 3005  79   3  12 0.00
Tue 08/18 20Z 0.15 3006  74   3  13 0.00
Tue 08/18 21Z 0.19 3007  72   4  12 0.00
Tue 08/18 22Z 0.23 3008  72   3  12 0.00
Tue 08/18 23Z 0.19 3108  75   3  12 0.00
Wed 08/19 00Z 0.19 3109  80   4  12 0.00
Wed 08/19 01Z 0.19 3109  83   4  12 0.00
Wed 08/19 02Z 0.15 3107  82   5  12 0.00
Wed 08/19 03Z 0.16 3007  82   7  12 0.00
Wed 08/19 04Z 0.18 2908  80   9  12 0.00
Wed 08/19 05Z 0.18 2908  78  12  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.44 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