NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260815_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 08/15 18Z 0.89 3209  87  27   9 0.00
Sat 08/15 19Z 0.57 3310  80  21   9 0.01
Sat 08/15 20Z 0.39 3311  75  19   9 0.00
Sat 08/15 21Z 0.21 3411  74  17   9 0.00
Sat 08/15 22Z 0.12 3410  76  14   9 0.00
Sat 08/15 23Z 0.07 3511  77  12   9 0.00
Sun 08/16 00Z 0.06 0010  76  12   9 0.00
Sun 08/16 01Z 0.07 0110  75  12   9 0.00
Sun 08/16 02Z 0.11 0209  71  12  10 0.00
Sun 08/16 03Z 0.11 0306  67  12  10 0.00
Sun 08/16 04Z 0.06 0403  67  14  10 0.00
Sun 08/16 05Z 0.04 0400  66  14  10 0.00
Sun 08/16 06Z 0.03 2100  66  15  10 0.00
Sun 08/16 07Z 0.03 2100  64  16  10 0.00
Sun 08/16 08Z 0.04 2301  63  15  10 0.00
Sun 08/16 09Z 0.04 2002  62  14  10 0.00
Sun 08/16 10Z 0.06 2103  62  12  10 0.00
Sun 08/16 11Z 0.07 2103  64  11  10 0.00
Sun 08/16 12Z 0.06 2004  65   9  10 0.00
Sun 08/16 13Z 0.07 1906  68   8  10 0.00
Sun 08/16 14Z 0.10 2007  71   7   9 0.00
Sun 08/16 15Z 0.16 2007  75   6  10 0.00
Sun 08/16 16Z 0.19 1907  78   6  10 0.00
Sun 08/16 17Z 0.12 1807  80   5  10 0.00
Sun 08/16 18Z 0.08 1809  80   4  11 0.00
Sun 08/16 19Z 0.09 1810  83   4  11 0.00
Sun 08/16 20Z 0.08 1812  85   4  11 0.00
Sun 08/16 21Z 0.14 1814  88   5  11 0.00
Sun 08/16 22Z 0.16 1915  92  15  12 0.01
Sun 08/16 23Z 0.20 1917  94  27  12 0.01
Mon 08/17 00Z 0.23 2019  96  39  12 0.01
Mon 08/17 01Z 0.25 2021  98  56  12 0.02
Mon 08/17 02Z 0.30 2024  98  74  12 0.03
Mon 08/17 03Z 0.32 2027  97  83  13 0.02
Mon 08/17 04Z 0.35 2028  97  87  13 0.01
Mon 08/17 05Z 0.35 2027  98  93  13 0.01
Mon 08/17 06Z 0.33 2026  98  93  13 0.01
Mon 08/17 07Z 0.32 2027  98  94  13 0.02
Mon 08/17 08Z 0.33 2027  98  94  13 0.02
Mon 08/17 09Z 0.35 2026  98  95  12 0.03
Mon 08/17 10Z 0.37 2026  98  90  12 0.02
Mon 08/17 11Z 0.34 2124  98  90  13 0.02
Mon 08/17 12Z 0.32 2122  98  87  13 0.02
Mon 08/17 13Z 0.30 2121  98  90  13 0.02
Mon 08/17 14Z 0.29 2119  98  91  13 0.02
Mon 08/17 15Z 0.26 2117  98  92  14 0.01
Mon 08/17 16Z 0.27 2115  99  94  14 0.01
Mon 08/17 17Z 0.25 2213  99  91  14 0.01
Mon 08/17 18Z 0.22 2210  99  88  14 0.01
Mon 08/17 19Z 0.21 2308  99  91  14 0.01
Mon 08/17 20Z 0.20 2407  99  88  14 0.01
Mon 08/17 21Z 0.20 2606  99  89  14 0.02
Mon 08/17 22Z 0.19 2806  99  90  14 0.01
Mon 08/17 23Z 0.19 3007  99  77  14 0.01
Tue 08/18 00Z 0.17 3108  97  51  14 0.01
Tue 08/18 01Z 0.16 3209  95  29  13 0.00
Tue 08/18 02Z 0.18 3210  96  28  13 0.01
Tue 08/18 03Z 0.15 3311  95  19  13 0.01
Tue 08/18 04Z 0.14 3411  96  13  13 0.02
Tue 08/18 05Z 0.09 3412  96   6  12 0.02

Run total areal avg QPF for the greens is: 0.48 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