NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260218_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 02/18 12Z 0.25 3015  81  53  -3 0.00
Wed 02/18 13Z 0.25 3118  71  60  -4 0.00
Wed 02/18 14Z 0.22 3117  64  64  -3 0.00
Wed 02/18 15Z 0.19 3115  57  59  -3 0.00
Wed 02/18 16Z 0.18 3114  50  52  -3 0.00
Wed 02/18 17Z 0.16 3213  44  51  -3 0.00
Wed 02/18 18Z 0.08 3311  39  48  -3 0.00
Wed 02/18 19Z 0.09 3209  37  45  -3 0.00
Wed 02/18 20Z 0.05 3308  36  39  -4 0.00
Wed 02/18 21Z 0.04 3408  39  36  -4 0.00
Wed 02/18 22Z 0.04 0008  38  21  -4 0.00
Wed 02/18 23Z 0.09 0109  33  13  -4 0.00
Thu 02/19 00Z 0.14 0211  29  12  -4 0.00
Thu 02/19 01Z 0.17 0311  28  16  -4 0.00
Thu 02/19 02Z 0.17 0312  28  20  -4 0.00
Thu 02/19 03Z 0.16 0311  29  21  -5 0.00
Thu 02/19 04Z 0.14 0211  28  27  -5 0.00
Thu 02/19 05Z 0.14 0212  27  32  -4 0.00
Thu 02/19 06Z 0.15 0211  26  35  -4 0.00
Thu 02/19 07Z 0.16 0311  26  40  -5 0.00
Thu 02/19 08Z 0.10 0207  25  52  -5 0.00
Thu 02/19 09Z 0.12 0306  21  58  -5 0.00
Thu 02/19 10Z 0.10 0405  20  57  -5 0.00
Thu 02/19 11Z 0.11 0405  19  60  -4 0.00
Thu 02/19 12Z 0.10 0405  19  53  -4 0.00
Thu 02/19 13Z 0.07 0503  19  43  -4 0.00
Thu 02/19 14Z 0.04 0601  19  40  -4 0.00
Thu 02/19 15Z 0.02 1100  21  38  -4 0.00
Thu 02/19 16Z 0.01 1700  25  44  -4 0.00
Thu 02/19 17Z 0.02 2001  29  49  -4 0.00
Thu 02/19 18Z 0.05 2102  34  55  -4 0.00
Thu 02/19 19Z 0.07 2103  38  55  -4 0.00
Thu 02/19 20Z 0.08 2104  40  49  -3 0.00
Thu 02/19 21Z 0.08 2104  44  47  -3 0.00
Thu 02/19 22Z 0.05 2003  50  50  -3 0.00
Thu 02/19 23Z 0.05 2004  59  47  -3 0.00
Fri 02/20 00Z 0.06 2004  68  41  -3 0.00
Fri 02/20 01Z 0.05 2003  75  42  -3 0.00
Fri 02/20 02Z 0.05 1905  80  49  -3 0.00
Fri 02/20 03Z 0.10 1908  85  47  -4 0.00
Fri 02/20 04Z 0.08 1907  90  37  -4 0.00
Fri 02/20 05Z 0.12 2009  93  34  -4 0.00
Fri 02/20 06Z 0.13 2009  93  27  -4 0.00
Fri 02/20 07Z 0.16 2011  92  23  -3 0.00
Fri 02/20 08Z 0.14 2010  88  21  -3 0.00
Fri 02/20 09Z 0.12 2010  83  23  -2 0.00
Fri 02/20 10Z 0.11 2009  82  24  -1 0.00
Fri 02/20 11Z 0.09 2007  84  27   0 0.00
Fri 02/20 12Z 0.06 1907  84  31   0 0.00
Fri 02/20 13Z 0.03 1807  83  35   0 0.00
Fri 02/20 14Z 0.02 1608  82  36   0 0.00
Fri 02/20 15Z 0.03 1610  81  46   0 0.00
Fri 02/20 16Z 0.05 1513  81  73   0 0.00
Fri 02/20 17Z 0.09 1515  86  92   0 0.00
Fri 02/20 18Z 0.13 1418  92  96   0 0.01
Fri 02/20 19Z 0.21 1322  95  95   0 0.04
Fri 02/20 20Z 0.25 1324  96  98   0 0.06
Fri 02/20 21Z 0.32 1326  95  99  -1 0.15
Fri 02/20 22Z 0.37 1226  95  99  -2 0.16
Fri 02/20 23Z 0.42 1225  95  99  -3 0.11

Run total areal avg QPF for the Central_Greens is: 0.53 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