Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260617_0000
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 06/17 00Z 0.50 2409  76  73   9 0.00
Wed 06/17 01Z 0.57 2410  73  68   9 0.00
Wed 06/17 02Z 0.62 2411  73  61   9 0.00
Wed 06/17 03Z 0.64 2411  76  48   9 0.00
Wed 06/17 04Z 0.56 2310  76  47   9 0.00
Wed 06/17 05Z 0.54 2311  76  50   9 0.00
Wed 06/17 06Z 0.54 2311  77  56   9 0.00
Wed 06/17 07Z 0.52 2311  76  58   9 0.00
Wed 06/17 08Z 0.48 2211  76  60   9 0.00
Wed 06/17 09Z 0.46 2212  76  62   9 0.00
Wed 06/17 10Z 0.41 2212  74  61   9 0.00
Wed 06/17 11Z 0.37 2112  74  58   9 0.00
Wed 06/17 12Z 0.35 2111  75  58   9 0.00
Wed 06/17 13Z 0.44 2110  74  60   9 0.00
Wed 06/17 14Z 1.39 2008  74  60   9 0.00
Wed 06/17 15Z 3.22 2108  73  64   9 0.00
Wed 06/17 16Z 3.75 2110  74  57   9 0.01
Wed 06/17 17Z 3.68 2110  70  53  10 0.01
Wed 06/17 18Z 1.64 1809  68  63  10 0.00
Wed 06/17 19Z 1.51 1809  70  74  11 0.00
Wed 06/17 20Z 1.98 2010  69  86  11 0.00
Wed 06/17 21Z 0.45 1808  71  76  11 0.01
Wed 06/17 22Z 0.14 1810  70  71  11 0.00
Wed 06/17 23Z 0.16 1811  72  68  11 0.00
Thu 06/18 00Z 0.27 1814  74  62  11 0.00
Thu 06/18 01Z 0.26 1815  75  52  11 0.00
Thu 06/18 02Z 0.39 1918  75  53  11 0.00
Thu 06/18 03Z 0.54 1921  76  55  11 0.00
Thu 06/18 04Z 0.56 1924  82  63  11 0.00
Thu 06/18 05Z 0.45 1925  81  72  11 0.00
Thu 06/18 06Z 0.49 2025  86  56  11 0.00
Thu 06/18 07Z 0.59 2027  89  56  11 0.00
Thu 06/18 08Z 0.51 2027  90  56  11 0.01
Thu 06/18 09Z 0.46 2027  94  92  11 0.05
Thu 06/18 10Z 0.37 1926  91  89  12 0.05
Thu 06/18 11Z 0.25 1832  90  69  12 0.00
Thu 06/18 12Z 0.19 1836  90  95  13 0.01
Thu 06/18 13Z 0.32 1840  89  98  13 0.01
Thu 06/18 14Z 0.31 1841  85  96  13 0.07
Thu 06/18 15Z 0.29 1842  96  96  13 0.07
Thu 06/18 16Z 0.30 1842  98  94  13 0.15
Thu 06/18 17Z 0.45 1937  98  93  13 0.17
Thu 06/18 18Z 0.48 1933  98  85  14 0.06
Thu 06/18 19Z 0.56 2031  98  79  14 0.04
Thu 06/18 20Z 0.61 2028  97  58  14 0.04
Thu 06/18 21Z 0.91 2224  95  84  14 0.16
Thu 06/18 22Z 0.82 2526  85  77  12 0.18
Thu 06/18 23Z 0.76 2624  88  78  12 0.01
Fri 06/19 00Z 0.80 2524  87  50  12 0.00
Fri 06/19 01Z 0.96 2526  91  50  11 0.00
Fri 06/19 02Z 1.06 2427  95  58  11 0.01
Fri 06/19 03Z 1.20 2528  96  62  10 0.01
Fri 06/19 04Z 1.23 2529  96  83   9 0.03
Fri 06/19 05Z 1.21 2530  97  92   9 0.05
Fri 06/19 06Z 1.41 2630  96  74   8 0.05
Fri 06/19 07Z 1.19 2631  94  65   7 0.01
Fri 06/19 08Z 0.97 2632  91  67   8 0.00
Fri 06/19 09Z 0.90 2732  91  61   9 0.01
Fri 06/19 10Z 0.86 2732  93  56   9 0.01
Fri 06/19 11Z 0.85 2731  92  56   9 0.01

Run total areal avg QPF for the Central_Greens is: 1.30 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