NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261010_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)
=== ===== === ==== ==== === === === ====
Sat 10/10 18Z 0.29 3209  65  38   1 0.00
Sat 10/10 19Z 0.19 3209  60  38   1 0.00
Sat 10/10 20Z 0.16 3209  54  36   2 0.00
Sat 10/10 21Z 0.15 3108  53  35   3 0.00
Sat 10/10 22Z 0.15 3007  52  35   4 0.00
Sat 10/10 23Z 0.13 3007  49  37   5 0.00
Sun 10/11 00Z 0.08 3106  44  39   6 0.00
Sun 10/11 01Z 0.09 2804  41  42   7 0.00
Sun 10/11 02Z 0.08 2403  38  45   7 0.00
Sun 10/11 03Z 0.08 2105  34  47   8 0.00
Sun 10/11 04Z 0.08 2006  32  47   9 0.00
Sun 10/11 05Z 0.09 2008  31  45   9 0.00
Sun 10/11 06Z 0.14 2011  34  44   8 0.00
Sun 10/11 07Z 0.16 2012  33  43   9 0.00
Sun 10/11 08Z 0.21 2113  33  44   9 0.00
Sun 10/11 09Z 0.19 2113  32  43  10 0.00
Sun 10/11 10Z 0.22 2115  32  44  10 0.00
Sun 10/11 11Z 0.22 2115  33  43  10 0.00
Sun 10/11 12Z 0.22 2115  35  39  10 0.00
Sun 10/11 13Z 0.23 2115  32  38  10 0.00
Sun 10/11 14Z 0.26 2116  37  37   9 0.00
Sun 10/11 15Z 0.22 2116  36  32  10 0.00
Sun 10/11 16Z 0.22 2016  39  27   9 0.00
Sun 10/11 17Z 0.17 1916  36  25   9 0.00
Sun 10/11 18Z 0.19 1917  41  39   8 0.00
Sun 10/11 19Z 0.20 1918  57  73   7 0.00
Sun 10/11 20Z 0.19 1918  77  95   6 0.00
Sun 10/11 21Z 0.19 1920  84  94   5 0.02
Sun 10/11 22Z 0.15 1822  92  95   6 0.06
Sun 10/11 23Z 0.12 1823  96  95   7 0.09
Mon 10/12 00Z 0.14 1823  97  92   7 0.07
Mon 10/12 01Z 0.14 1920  97  95   8 0.08
Mon 10/12 02Z 0.14 1916  97  95   8 0.11
Mon 10/12 03Z 0.12 1913  96  96   8 0.10
Mon 10/12 04Z 0.11 1810  95  97   9 0.06
Mon 10/12 05Z 0.10 1806  95  98   9 0.05
Mon 10/12 06Z 0.09 1703  96  98   9 0.05
Mon 10/12 07Z 0.07 1701  95  96   9 0.03
Mon 10/12 08Z 0.07 2401  95  90   9 0.01
Mon 10/12 09Z 0.06 3103  96  85   9 0.01
Mon 10/12 10Z 0.03 3407  97  80   9 0.01
Mon 10/12 11Z 0.02 3510  98  80   8 0.01
Mon 10/12 12Z 0.03 3513  98  79   8 0.01
Mon 10/12 13Z 0.05 3515  97  70   8 0.00
Mon 10/12 14Z 0.06 3415  96  52   8 0.00
Mon 10/12 15Z 0.06 3415  93  29   9 0.00
Mon 10/12 16Z 0.12 3316  90  24  10 0.00
Mon 10/12 17Z 0.11 3317  83  40  11 0.00
Mon 10/12 18Z 0.23 3221  90  60   9 0.00
Mon 10/12 19Z 0.26 3220  90  64   9 0.01
Mon 10/12 20Z 0.25 3221  90  72   9 0.01
Mon 10/12 21Z 0.26 3221  94  80   8 0.01
Mon 10/12 22Z 0.25 3221  98  84   7 0.01
Mon 10/12 23Z 0.16 3320  98  81   7 0.01
Tue 10/13 00Z 0.10 3318  98  81   7 0.01
Tue 10/13 01Z 0.03 3515  97  86   6 0.00
Tue 10/13 02Z 0.04 3511  97  91   6 0.00
Tue 10/13 03Z 0.05 0008  97  96   6 0.00
Tue 10/13 04Z 0.02 3506  97  98   6 0.00
Tue 10/13 05Z 0.04 0103  97  96   6 0.01

Run total areal avg QPF for the Central_Greens is: 0.84 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