NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260514_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)
=== ===== === ==== ==== === === === ====
Thu 05/14 12Z 0.07 1811  98 100   4 0.00
Thu 05/14 13Z 0.10 1809 100  99   3 0.02
Thu 05/14 14Z 0.09 1906 100  95   3 0.02
Thu 05/14 15Z 0.03 1603 100  79   3 0.02
Thu 05/14 16Z 0.05 1403 100  63   4 0.01
Thu 05/14 17Z 0.08 1304 100  69   4 0.02
Thu 05/14 18Z 0.07 1302 100  85   4 0.03
Thu 05/14 19Z 0.08 0300 100  95   4 0.04
Thu 05/14 20Z 0.07 3504  99  98   4 0.06
Thu 05/14 21Z 0.08 0105  98  97   4 0.09
Thu 05/14 22Z 0.08 3506  96  94   4 0.10
Thu 05/14 23Z 0.07 0007  94  94   4 0.05
Fri 05/15 00Z 0.14 0208  94  94   4 0.04
Fri 05/15 01Z 0.24 0410  94  92   4 0.07
Fri 05/15 02Z 0.36 0611  92  92   4 0.09
Fri 05/15 03Z 0.47 0614  95  91   3 0.04
Fri 05/15 04Z 0.60 0718  98  93   3 0.05
Fri 05/15 05Z 0.67 0718  99  90   3 0.06
Fri 05/15 06Z 0.61 0917  99  85   3 0.05
Fri 05/15 07Z 0.65 0920  98  89   3 0.07
Fri 05/15 08Z 0.59 0919  96  95   3 0.04
Fri 05/15 09Z 0.60 0920  96  95   3 0.04
Fri 05/15 10Z 0.59 0919  97  96   3 0.03
Fri 05/15 11Z 0.60 0919  97  97   3 0.04
Fri 05/15 12Z 0.61 0818  97  93   3 0.03
Fri 05/15 13Z 0.58 0817  96  78   3 0.01
Fri 05/15 14Z 0.49 0813  95  76   3 0.00
Fri 05/15 15Z 0.46 0810  95  74   3 0.00
Fri 05/15 16Z 0.43 0707  96  66   3 0.00
Fri 05/15 17Z 0.26 0704  96  57   3 0.00
Fri 05/15 18Z 0.15 0401  95  53   4 0.01
Fri 05/15 19Z 0.11 3501  93  46   4 0.01
Fri 05/15 20Z 0.16 3002  92  40   4 0.01
Fri 05/15 21Z 0.24 2904  89  41   4 0.01
Fri 05/15 22Z 0.27 2904  85  42   5 0.00
Fri 05/15 23Z 0.27 2905  85  30   5 0.00
Sat 05/16 00Z 0.29 2806  87  26   5 0.00
Sat 05/16 01Z 0.43 2609  93  31   5 0.00
Sat 05/16 02Z 0.50 2511  96  33   5 0.00
Sat 05/16 03Z 0.54 2513  96  32   5 0.01
Sat 05/16 04Z 0.53 2513  94  33   5 0.01
Sat 05/16 05Z 0.54 2515  94  41   5 0.01
Sat 05/16 06Z 0.61 2616  93  54   5 0.01
Sat 05/16 07Z 0.62 2618  90  54   5 0.00
Sat 05/16 08Z 0.57 2618  84  46   5 0.00
Sat 05/16 09Z 0.55 2718  81  21   5 0.00
Sat 05/16 10Z 0.61 2819  80  23   4 0.00
Sat 05/16 11Z 0.67 2720  78  17   4 0.00
Sat 05/16 12Z 0.73 2721  79  22   4 0.00
Sat 05/16 13Z 0.73 2620  77  17   4 0.00
Sat 05/16 14Z 0.73 2618  72  11   5 0.00
Sat 05/16 15Z 0.76 2616  63  21   6 0.00
Sat 05/16 16Z 0.89 2513  55  18   6 0.00
Sat 05/16 17Z 1.16 2513  63  37   7 0.00
Sat 05/16 18Z 1.94 2415  74  40   7 0.00
Sat 05/16 19Z 4.90 2316  76  13   7 0.00
Sat 05/16 20Z 8.22 2318  77  22   7 0.00
Sat 05/16 21Z 5.79 2420  79  19   8 0.00
Sat 05/16 22Z 1.72 2422  78  38   9 0.00
Sat 05/16 23Z 1.07 2423  76  35   9 0.00

Run total areal avg QPF for the Central_Greens is: 1.20 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